Goals from substitutes Gabriel Martinelli and Leandro Trossard gave Arsenal a perfect start to their Champions League campaign in Bilbao.
Whether you were at the game or following from elsewhere, we want to know what you learned.
Get in touch with your views here
Come back to this page on Wednesday to find a selection of your replies
Arsenal boss Mikel Arteta makes just one change from the side that beat Nottingham Forest, as Declan Rice comes in for Martin Odegaard.
There's also a boost as William Saliba is fit enough to be on the bench.
Arsenal XI: Raya, Timber, Mosquera, Gabriel, Calafiori, Zubimendi, Rice, Merino, Madueke, Eze, Gyokeres.
Subs: Arrizabalaga, Setford, Saliba, Hincapie, Martinelli, Norgaard, Trossard, Nwaneri, Lewis-Skelly, Dowman.
Athletic Club XI: Unai Simon, Gorosabel, Vivian, Paredes, Adama, Vesga, Jauregizar, Williams, O Sancet, Navarro, Berenguer.
Subs: M Santos, Padilla, Guruzeta, Areso, Lekue, Galarreta, Yuri, Unai G, Maroan, Nico Serrano, Regi, Jon De Luis.
There are six games in the Champions League on Tuesday, two of them involving Premier League teams, and BBC Sport will bring you every moment.
Athletic Bilbao v Arsenal (17:45) - listen on BBC Radio 5 Live
PSV Eindhoven v Union Saint-Gilloise (17:45)
Benfica v Qarabag
Juventus v Borussia Dortmund
Real Madrid v Marseille
Tottenham v Villarreal - listen on BBC Radio 5 Live
Kick-off times 20:00 BST unless stated
Follow all of the action and reaction here
You can also listen to today's Radio 5 Live Champions League commentaries on most smart speakers. Just say "ask BBC Sounds to play Athletic Bilbao v Arsenal" or "ask BBC Sounds to play Tottenham v Villarreal".
There will also be a Champions League Match of the Day on BBC One on Wednesday, from 22:40 to 00:00.
Image source, Getty Images
Chief football writer Phil McNulty has been answering your questions.
Yemi asked: if you had to label one of the English teams as a dark horse - that could surprise everyone beyond that of the favourites Liverpool - which team would it be and for what reason?
Phil answered: I would say Arsenal because they reached the semi-finals last season and have added some real quality in the transfer window.
The experience of the last Champions League campaign will serve them well and they now have the strength of squad to finally break through and win one of the major trophies.
Do I think Arsenal will win the Champions League? Not so sure about that, but I think they can make a real impact.
Follow Phil's Q&A and the rest of the day's football news on our daily live page
Watch BBC Radio 5 Live's Monday Night Club panel discuss Arsenal and the recent impressive performances by new signing Noni Madueke.
"He was really refreshing," said former Newcastle goalkeeper Shay Given.
"The biggest thing is he had end product to most things. I'm actually surprised Chelsea let him go."
"There was a negativity around Madueke's signing," added The Observer's Rory Smith.
"I wonder to what extent it was because at that point Arsenal fans just wanted to sign a striker.
"If they had signed Viktor Gyokeres first I wonder if the reaction would have been different."
Watch the full episode on BBC iPlayer and listen on BBC Sounds
Laura Kirk-Francis
Fan writer
Image source, Getty ImagesMartin Zubimendi's arrival at Arsenal in July was perhaps not accompanied by the fanfare it deserved. The transfer was rumoured to have been agreed at the start of the year, so the signing of the Spaniard always seemed like a formality rather than an exciting surprise.
Before his display against Nottingham Forest, Zubimendi had enjoyed an encouraging start to the season. But it was his double on Saturday that really announced himself to the Premier League.
His first was simply a moment of magic, the exact type that Arsenal were undone by at Anfield in August.
In the first three weeks of the season, Arsenal had created the second-lowest xG in open play in the league. But on Saturday, chances were flowing and Zubimendi's effort showcased the exact technical brilliance that highlighted why Mikel Arteta was so keen to bring him to the club.
You cannot overstate the difficulty of the volley that sailed past goalkeeper Matz Sels. For many others, it would have simply rocketed over the crossbar.
The Spaniard rounded off his day with a header at the back post which sealed the game. Certainly not the tallest of Arsenal players, this is another string to Zubimendi's bow that make him one of the most versatile players this season.
When Arsenal announced the signing, their video sought to showcase his ability to control the tempo of games, knowing when to speed things up and slow things down. The video shows the player speaking over a drumbeat and a metronome.
Saturday was a perfect example of Zubimendi's ability to dictate play from the heart of midfield. Add in his two goals and he is doing exactly what Arsenal need him to do and more.
Find more from Laura Kirk-Francis at the Latte Firm podcast, external
Image source, Getty ImagesOpta's supercomputer has Arsenal as second favourites to win this season's Champions League.
The model estimates the probability of each match outcome (win, draw or loss) by using betting market odds and Opta's own power rankings. Both these areas are based on historical and recent team performances and the computer runs 10,000 simulations to create its predictions.
Having reached the semi-finals last time out, Mikel Arteta's side win the tournament in 18% of simulations, suggesting another strong campaign for the Gunners.
Image source, OptaThe Gunners have the second-easiest draw according to Opta's power rankings, with only Copenhagen ranked to have a 'easier' league phase.
Therefore, the supercomputer has Arsenal reaching the quarter-finals in 68% of simulations, matching last season's run 44.8% of the time and going one step further to the final more than a quarter of the time.
Having played the most European Cup/Uefa Champions League games without ever lifting the trophy (211), they will be hoping to change that this time.
Opta ranks the likeliest threats to Arsenal as favourites Liverpool (20.4%), and PSG (12.1%).
Scouts from Arsenal, Chelsea, Manchester United, Barcelona and Real Madrid have all been watching Ajax's 17-year-old Belgian midfielder Jorthy Mokio. (Caughtoffside), external
Want more transfer stories? Read Tuesday's full gossip column
Alex Howell
Arsenal reporter in Bilbao
Image source, AFP via Getty ImagesMikel Arteta has said he is excited to "start from scratch" as Arsenal prepare to play Athletic Bilbao in their first Champions League game of the season.
The Gunners reached the semi-final stage of the competition last season, losing to eventual winners Paris St-Germain.
Arsenal beat Athletic Bilbao 3-0 in their final pre-season game of the summer, but have some injury worries coming into this fixture.
Captain Martin Odegaard came off with a shoulder problem in the win over Nottingham Forest on Saturday and has not travelled to Spain.
The Gunners are also going to be without Bukayo Saka and Ben White, who has a minor issue and did not train.
However, Arsenal have been given a boost as William Saliba is back in the squad after missing the match on Saturday with an ankle problem.
Image source, Getty ImagesDavid Raya says Arsenal have "belief" they can win the Champions League after suffering a painful defeat by eventual winners Paris St-Germain in the semi-finals last season.
The Spain international goalkeeper - who turned 30 on Monday - has kept 42 clean sheets in his 100 Gunners appearances but has not lifted a major trophy with the club despite his impressive impact.
"We have belief, we want to win," he told media before Tuesday's Champions League opener against Athletic Bilbao.
"We are Arsenal and we play to win. It is not a doubt, that is what we play to do. That is what we play football for.
"It's a long journey, a long season, in the Premier League and Champions League so we are focused in the present.
"We want to go higher this season, that's what we want to do."
When pushed on what the Gunners learned from that PSG defeat, Raya added: "That it hurts a lot losing in the semi-final. You get more mature.
"It is incredible to be here."
Kepa Arrizabalaga became Arsenal's first full-time goalkeeper signing since Raya when he joined from Chelsea in the summer, and his compatriot is relishing the challenge.
"Competition is all over the place, you need competition to get out the best [in yourself]," Raya added.
"Kepa and me, we have a good relationship. It's a pleasure to share dressing room with him."
Arsenal boss Mikel Arteta has been speaking to the media before Tuesday's Champions League game against Athletic Bilbao (17:45 BST).
Here are the key lines from his news conference:
Gabriel Martinelli, Kai Havertz, Ben White and captain Martin Odegaard will all miss the Gunners' Champions League opener. He added that Odegaard has not travelled with the squad.
Providing an update on Bukayo Saka's fitness, Arteta said: "There's still quite a lot of things to go through. Very difficult to understand what week he is going to be available. He will most certainly be pushing to be available as soon as possible."
Asked if Arsenal are better placed to win the Champions League now: "That's the aim in the beginning but we all know it's going to be a really long journey. The margins in this competition are very small and you have to be at your very best from day one to give yourself the best chance."
What has the team learned from last season? "That we are good enough, that we can compete against any opposition on the day. You have to have two things go your way. You have to have a full squad available at critical moments and have to put the ball in the net when the chances come your way."
More on last season's run to the semi-final: "We were very unlucky in the semi-final not to get through. You take a lot of learning from that, it's not only what we feel but the expectations that we have created and the real conviction that we can go all the way. We showed a very good level of consistency throughout the competition and we need to lean on that and try to be better."
He is "excited" to begin a new European campaign in the area where he grew up: "A beautiful place and stadium we know is going to create something special."
Listen to live commentary of Athletic Bilbao v Arsenal on Tuesday from 17:45 on BBC Sounds
Image source, Getty ImagesAthletic Bilbao coach Ernesto Valverde thinks Arsenal are one of the favourites to win the Champions League this season, speaking ahead of his side's fixture against the Gunners on Tuesday.
"Arsenal are totally focused on this match," said Valverde. "They are one of the favourites to win the Champions League because of their skill, tactics, and the winning spirit their coach Mikel Arteta has given them.
"It's the start of the Champions League and we're playing against a high-level opponent, the kind that Bilbao likes, but we have to be very careful and take advantage of opportunities. Arsenal won't be forgiving."
Bilbao forward Inaki Williams added "We are playing against a great team, one that shows no mercy. We have to make the most of the chances we get."
Alex Howell
Football reporter
Image source, Getty ImagesWilliam Saliba looks to be in contention for Arsenal's opening Champions League game with Athletic Bilbao on Tuesday.
The France centre-back missed Saturday's 3-0 win over Nottingham Forest. He did train with the team before that match, but said to manager Mikel Arteta he felt he needed some more time.
In the pictures of Monday's training session that are available, it does not look like Bukayo Saka, who is missing with a hamstring injury, or Martin Odegaard, who came off with a shoulder problem on Saturday, were in the session with the main group.
We asked for your thoughts after Saturday's Premier League game between Arsenal and Nottingham Forest.
Here are some of your comments:
Arsenal fans
Mike: Very confident display and showed the great benefit of Arsenal's active transfer period. The new boys all acquitted themselves extremely well. Keep up this excellent start and we will have a real chance of total success.
Vince: What a complete victory and to think the new boys haven't had much time to bed in. If all goes well, the second half of the season should prove to be great watching for us Gooners!
Ryan: Last year, losing Saka, Havertz, Saliba and Odegaard (plus no Rice) would have probably led to a shaky win or, more likely, dropped points. The strength in the squad now means that four definite starters are not missed. Get through this tough first three months of the season close to the top and Arsenal will be in good shape.
Barry: With the players we now have, barring too many injuries, this could be our time to win the league.
Phoenix: A good way to forget the loss at Anfield - good ball play from the guys. Just happy for Viktor Gyokeres and Zubimendi is a colossus of a player - small in nature, big in performance. Trophy is the currency that the team needs going forward.
Forest fans
Andre: I was expecting a larger defeat, to be honest. We need to bring in the new signings. Never been a fan of our new coach. Seems he is doing the same job when he was at Tottenham - taking us down the league!
Stephen: Forest haven't won at the Emirates for a while. No Ange effect either. Needs to start winning big time with all the new recruitments.
Mossy: Losing players this early in the season does not bode well, with games coming up quick and fast. Morgan Gibbs-White and Callum Hudson-Odoi are shadows of the influential players of last season.
Steve: This is a disaster appointment by an owner who had a mardy and dumped our best manager for years!
Russell: Let's have some patience - Arsenal are a top side.
Arsenal, Barcelona and Napoli are interested in Palmeiras' 19-year-old Brazilian centre-back Luiz Gustavo Benedetti. (Mundo Deportivo - in Spanish), external
Want more transfer stories? Read Monday's full gossip column
Alex Howell
Arsenal reporter
The physical demands on players and relentless schedule meant Mikel Arteta and the club decided they needed to bring in high-calibre players to ensure there was not a drop in quality during times like this.
Kai Havertz has a knee injury that will keep him out for weeks, Bukayo Saka has been unavailable since the 5-0 win over Leeds with a hamstring injury, while centre-back William Saliba was withdrawn with an ankle problem in the defeat at Liverpool.
Midfielder Martin Odegaard has had a shoulder problem and was again withdrawn against Nottingham Forest after an awkward fall.
The absence of this quartet would usually be a cause for crisis at Arsenal, and injuries to their influential players last season was a major factor in why the Gunners fell away in the title race to finish second behind Liverpool and falter in the Champions League semi-final against Paris St-Germain.
While Arteta will be eager for those players to return, his side - led by impressive England duo Noni Madueke and Eberechi Eze - proved they have the talent and options to cope and get results after their 3-0 victory over Forest on Saturday.
When asked about his summer recruitment, the Spaniard said: "If we wouldn't have done that and, as you said, with the injuries that we have, unfortunately some of them are very difficult to control, we would have been in a very different place.
"We knew that that was the standard, that's the standard of the other teams in the league in Europe, and you can see that.
"I'm very happy because it gives us options, it gives us the capacity as well to change games, it gives the capacity to have presence in the team, and now we have to make sure that everybody feels connected and important."
Arsenal travel to Spain on Tuesday to face Athletic Bilbao for the first of their Champions League games this season and Arteta said that was another reason the club decided to invest.
"The players have to play 70 or 74 games throughout the season. It's never been done," he added.
"When the intensity was that high, they are not going to be able to sustain that. So you need more players, the standards have raised, we need better players and there's no secret."
It was a sentiment backed up by former Arsenal defender Martin Keown.
"That was a real scary show of strength from Arsenal, with the quality of player. You've been without Havertz, and Saka unavailable, and that was a problem for Arsenal last season, but not this," he told TNT Sports.
"Madueke, Eze coming in today, both of them outstanding. [Viktor] Gyokeres, what about that second goal, so direct, forward pass. This man in the box, a real predator.
"The quality of the group, even this young man [Cristhian Mosquera] at the back, what a performance that was. His full debut at Arsenal, home game, outstanding.
"At the moment, Arsenal are looking so strong."
Pundits Ashley Williams and Shay Given join host Mark Chapman to bring you the action and talking points from Saturday's Premier League fixtures.
And listen back to full match commentaries on BBC Sounds:
Alex Howell
Arsenal reporter
Image source, Getty ImagesArsenal were criticised for their performance in the loss against Liverpool before the international break, but they brushed off that disappointment to dominate against Nottingham Forest.
In response, Mikel Arteta named an attacking side with Eberechi Eze and Noni Madueke either side of striker Viktor Gyokeres.
In midfield, Mikel Merino was handed a start, after scoring a hat-trick against Turkey for Spain while on international duty, alongside Martin Odegaard as Arsenal looked to take control of the game.
Martin Zubimendi, there to link up the play, scored two goals in the same game for the first time in his top-flight club career.
Madueke, fresh from scoring his first England goal, continued that good form and was the Gunners' standout player.
He was positive whenever he was on the ball and provided an outlet for his team. And Forest, following an injury to Murillo, moved Neco Williams to left-back in an attempt to keep Madueke quiet.
Madueke was replaced to a standing ovation while the supporters inside the stadium sang his name.
Cristhian Mosquera started alongside centre-back Gabriel in place of William Saliba, who is continuing his recovery from an ankle problem, and also put in an impressive performance.
David Raya also reached a milestone as he made his 100th appearance for Arsenal and kept his 42nd clean sheet.
