Champions League holders Paris Saint-Germain stunned Barcelona with a 90th-minute Goncalo Ramos winner to claim a 2-1 away victory in the league stage on Wednesday.
Ferran Torres sent hosts Barcelona ahead with a cool finish but Senny Mayulu fired a depleted PSG level before halftime.
Ramos came off the bench and struck in the final minute at the Olympic stadium as the reigning European champions made it two wins from two in this season's league phase.
It was an even and thoroughly entertaining bout between two of the competition's favourites at the Olympic stadium which was eventually settled by Ramos' late strike, as PSG exploited Barca's high defensive line.
Hansi Flick selected Torres over veteran striker Robert Lewandowski and also benched Ronald Araujo for Eric Garcia, after the Uruguayan's red card against PSG in 2024.
PSG coach Luis Enrique, who won the treble with Barcelona in 2015, was lacking several key players and his team held on at times but eventually got the better of last season's semifinalists.
Barcelona and PSG have not been on the best of terms over the past decade, with the Catalans recording one of the greatest comebacks in the history of the game in 2017 with a 6-1 win over the Parisians.
STARS MISSING FOR PSG
PSG snatching Neymar and going on to sign all-time Barca great Lionel Messi worsened relations, although Luis Enrique's approach and a spate of injuries left the visitors shorn of star names on their return to Catalonia.
Ballon d'Or winner Ousmane Dembele and his usual attacking partners Desire Doue and Khvicha Kvaratskhelia all missed out, but PSG midfielders Vitinha and Fabian Ruiz were fit to start despite doubts leading up to the game.
From kick-off Barca starlet Lamine Yamal was out to prove a point. After finishing as runner-up behind Dembele, the teenager started stating his case for next year's award.
Yamal pirouetted away from two defenders and dodged Nuno Mendes as a statement of intent, starting an enthralling battle with PSG's left-back.
The defender shut him down for Portugal in the Nations League in the summer and managed to dispossess the winger in the box a few minutes later to strike back in their individual tussle.
Yamal created the first clear chance with a sensational pass using the outside of his boot to send Torres through.
The Spaniard rounded goalkeeper Lucas Chevalier but Illia Zabarnyi slid in to block his goal-bound effort.
Barcelona took the lead in the 19th minute after Yamal and Pedri combined quickly and Torres slotted home from Marcus Rashford's quick first-time pass.
On loan from Manchester United, Rashford has created goals in each of his last four Barcelona appearances.
After half an hour PSG started to grow into the game and forced Wojciech Szczesny into his first save, tipping Achraf Hakimi's free-kick around the post.
MARAUDING MENDES
Mendes gave Yamal a taste of his own medicine by blazing away from the youngster and downfield, cutting through Barcelona players, only to be felled by a desperate Frenkie de Jong.
It showed the defender's pace was the best way to hurt Barca and Mendes repeated the trick to set up the equaliser.
Mendes ripped into Barca territory and Pau Cubarsi misjudged a lunge to try and cut out his pass for 19-year-old striker Mayulu, who beat Szczesny from just inside the area in the 38th minute.
Bradley Barcola fired narrowly over and then forced Szczesny into a solid save either side of the interval as the European champions clicked into a higher gear.
PSG were fortunate Mendes was not issued a second yellow for felling Yamal in full flow on the edge of the box as the pendulum swung back the other way.
Dani Olmo's shot was cleared off the line by Hakimi and PSG's Kang-in Lee curled against the post as the clock ticked down in an even second half.
Eventually Ramos grabbed three points for PSG as he stayed onside to collect Hakimi's pass, after the Moroccan got in behind Barca's defence, and tap home.