Ramsey opens scoring for Gunners, Torreira shot deflects in off Koulibaly
Alonso heads in for Chelsea with five mins to go in Prague
Hazard & Kante come off bench for Blues in second half
Benfica beat Eintracht Frankfurt & Valencia win at Villarreal in other ties
That is that.
A good night's work for the English clubs in the Europa League.
Ties over?
Click here for Emlyn Begley's report on Arsenal's win
And click here for Mantej Mann's report on Chelsea's victory.
BBC Football live text will return.
Arsenal 2-0 Napoli
Arsenal manager Unai Emery: "The first 90 minutes here we can impose a big plan. They can control ball with possession. They had one chance in the first half then two chances in second half.
"We deserved a third goal.
"Away there is going to be different. We need to be focused and clear. No more confident than we need."
Arsenal 2-0 Napoli
Napoli coach Carlo Ancelotti speaking to BT Sport: "We didn't start well. The first half was not good and difficult to come back. The result is difficult to change but we have 90 minutes again.
"There were two different games [tonight]. The first half we were really bad.
"We will try to play 90 minutes in Napoli.
"The two goals we conceded were from two mistakes. We were a little bit worried at the beginning. Fortunately we have the possibility to change that at home.
"We could score one goal [tonight], but it's 2-0 and we have to think about the next game.
"We are totally confident [to turn the match around] with our supporters in our own stadium."
Villarreal 1-3 Valencia
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It was quite a match at Villarreal - two Valencia goals in stoppage time!!
Arsenal 2-0 Napoli
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#bbcfootball
Dylan Lingham: Watching Napoli tonight confirms why Juventus always win Serie A. They are the second best team in Italy and have been absolutely dreadful. Sloppy passing, giving the ball away cheaply and can't finish off attacks.
Arsenal 2-0 Napoli
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Arsenal 2-0 Napoli
Arsenal midfielder Aaron Ramsey to BT Sport: "To keep a clean sheet and score a couple of goals is a lovely way to start the first leg. We’re delighted with that.
"We suffered a lot. They’re a good team and keep the ball well. We had to dig in.
"I should have scored in the second half again. We can go into the second leg with a little bit of a cushion. But we know it will be a difficult place to go.
"They were unlucky not to go through [in the Champions League]. They are a quality team. They’re a tough team to play against. We have given ourselves a great opportunity."
Image source, Reuters#bbcfootball
Zak: good to see both Arsenal and Chelsea winning, although I have to ask whether Insigne was born in an offside position or he is ignoring the offside rule for the fun of it.
Slavia Prague 0-1 Chelsea
Chelsea prevented three people from entering the stadium for Thursday's Europa League quarter-final at Slavia Prague after a video appeared to show them making abusive comments about Liverpool forward Mohamed Salah.
Liverpool said the video shows "vile discriminatory chants" and is "dangerous and disturbing."
Three of the six people in the video were identified and barred.
Chelsea are working to identify the other three, who did not turn up.
The Stamford Bridge club are working with police and the other three individuals face bans if they are found to be season ticket holders or members.
Liverpool said they are working with Merseyside Police and Chelsea.
Arsenal 2-0 Napoli
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All over in Spain and Portugal.
Valencia have won 3-1 at Villarreal - the winners of this tie face Arsenal or Napoli in the semi-finals - while Benfica have triumphed 10-man Eintracht Frankfurt 4-2 in Lisbon where teenager Joao Felix is taking home the match ball after a brilliant hat-trick.
Image source, Getty Images
Image source, EPAArsenal 2-0 Napoli
A superb win for the Gunners who, perhaps more importantly, prevent the Italian side of grabbing an away goal - they did have their chances.
Image source, ReutersVillarreal are sinking faster than a yellow submarine!
Goncalo Guedes make it 3-1 to visitors Valencia.
Late, late drama in Spain.
Slavia Prague 0-1 Chelsea
There are no seconds remaining.
Chelsea pinch it.
It wasn't vintage Blues, but it was vintage Sarri.
Image source, Getty ImagesSlavia Prague 0-1 Chelsea
There are (a minimum of) 20 seconds remaining at the Eden Arena.
Who said the Europa League was lacking drama?
A stunner from great Dane Daniel Wass puts Valencia 2-1 ahead at Villarreal in the dying moments.
That could be crucial.
Image source, Getty ImagesStoppage o'clock in London and Prague.
Arsenal 2-0 Napoli
Arsenal are hanging on to their two-goal lead a little.
Adam Ounas speeds down the right after latching on to Kalidou Koulibaly ball from deep.
However, his shot from an angle is blocked by Petr Cech at his near post.
Moments later, parts of the stadium erupt as Pierre-Emerick Aubameyang fires a shot that has the net rippling, but as a result of it hitting it at the side.
Image source, ReutersArsenal 2-0 Napoli
Lorenzo "Offside" Insigne is replaced by Amin Younes and Piotr Zielinski makes way for Adam Ounas.