Zlatan Ibrahimovic produced an inspired display as Paris Saint Germain struck late to deny Barcelona in a thrilling draw in the Parc de Princes.
After Sergio Busquets hit his own post in denying Ezequiel Lavezzi, Dani Alves' delicious pass allowed Lionel Messi to hand the Catalans a half-time lead.
But the Argentine was replaced by Cesc Fabregas with a hamstring injury at the break, and took with him much of Barca's composure in Tito Vilanova's first game in the dugout for over two months following treatment on a throat tumour.
The returning Spanish boss had cause for concern 11 minutes from time as Ibrahimovic, who departed the Nou Camp in acrimonious circumstances in 2011, reacted quickest to equalise after Thiago Silva's header crashed off the post.
Replays suggested the Swedish striker was offside in the build-up, but Barca's sense of injustice lasted just 10 minutes as Salvator Sirigu tripped Alexis Sanchez in the penalty area, with Xavi sending the Italian stopper the wrong way with a consummate spot kick.
However, PSG had the final say with the last kick of the game in stoppage time as Ibrahimovic's header found Blaise Matuidi, whose shot deflected off Marc Bartra and beyond the despairing Victor Valdes.
The French league leaders' late goal hands them a glimmer of hope going into the second leg in Barcelona, who are sweating over the fitness of Messi. His hamstring strain could keep him out of the return game as well as a possible semi-final.
"[Messi] will be a major loss because he is the best player in the world, but we have a big squad, and good players, and will try to win the tie."
In the other quarter final on Tuesday, Bayern Munich took a significant step towards avenging their defeat on penalties in last year's final by sweeping aside Juventus 2-0 at the Allianz Arena.
One of only two sides still unbeaten in the competition before kick-off, the Italians fell behind inside 30 seconds when David Alaba's long range strike beat Gianluigi Buffon.
Substitute Arjen Robben was denied by Buffon as Juve weathered the storm, but when Luiz Gastavo's shot was only parried as far as Mario Mandzukic, the Croat squared for Thomas Mueller to tap home.
Bayern coach Jupp Heynckes told Sky: "We were very well prepared for this match.
"You could see that in our tactics. We attacked them very early and took Pirlo out of the game collectively. The early goal gave us safety and we played amazingly at some points after that.
"I studied Juventus over and over again. We are happy to have won the match against an Italian without conceding. We played high-class football. We controlled and dominated the match. And against the Italian champions. I must compliment my team."