Highlights: Monaco 2-1 Barcelona
Nigerian striker George Ilenikhena scored on his Champions League debut as Monaco produced an upset against 10-man Barcelona.
The 18-year-old substitute raced on to Vanderson's long ball over the top of the defence in the 71st minute and blasted his shot past Marc-Andre ter Stegen.
Eric Garcia had earlier been shown a straight red card with just 10 minutes gone when he fouled Takumi Minamino as the last man after a poor pass out from the back by Ter Stegen.
Monaco took the lead soon after when Maghnes Akliouche slotted past Ter Stegen who was rooted to the spot.
Barcelona's own teenage star Lamine Yamal equalised with his first Champions League goal when he latched on to a long ball and cut inside before drilling a low shot into the bottom corner.
But Ilenikhena's goal, his first since signing from Royal Antwerp in the summer, condemned Barcelona to an opening defeat.
Vanderson's strike from the edge of the area was pushed past the post while Minamino had an effort deflected on to the crossbar for the hosts.
It could have been a more emphatic win but Folarin Balogun had a penalty overturned late on following a video assistant referee (VAR) check after he was adjudged to have gone down too easily under the challenge of Inigo Martinez.
Ilenikhena outshines Yamal as teenagers make history
Ilenikhena came off the bench in the 59th minute and was on the scoresheet 12 minutes later to earn victory for his new side.
The youngster's composed finish put him among esteemed company after he set a record for Monaco's youngest Champions League goalscorer (18 years and 34 days), breaking Kylian Mbappe's mark (18 years and 63 days) set in February 2017.
He is also the first player in the competition’s history to score against the same side in successive games but for different teams, having previously netted for Antwerp last December.
Yamal, who has had an incredible year after winning the European Championship with Spain, took 11 Champions League appearances to register his first goal in the competition as he put in another impressive performance despite his side's defeat.
He has now made the most appearances by a player aged 17 or under in the competition’s history.
Yamal scored in two consecutive games for the first time for Barca and became the second youngest goalscorer in Champions League history (17 years and 68 days), second only to team-mate Ansu Fati (17 and 40 days) in December 2019.
The 17-year-old also became the youngest Ballon d'Or nominee when the shortlist was announced earlier this month.
'What a moment!' - Akliouche puts Monaco ahead against Barcelona
Yamal nets first Champions League goal
Watch highlights of every Champions League game from 22:00 on Wednesday on BBC iPlayer and the BBC Sport website and app.
There will also be a Champions League Match of the Day on BBC One on Wednesday, from 22:40 to 00:00.
