The goal wasn't his fault. Busi was covering the left wing and Ibra dropped back to get the ball and had no one marking him. Adriano came out to pressure him and he knew there was no striker and Pique was there to sweep up. So that was the correct decision. Pastore came on the overlap at which point he kind of had two players to deal with, but again he had Pique to sweep up. Where it went wrong was that Busi decided to play the offside trap instead of just running back ahead of his player. This put Pique in two minds and he played the offside trap but that gave Pastore a free run on goal.
As for his performance, he did ok overall, especially considering he's just come back from injury. He had some good moments bringing the ball out from the back. And for once the defence was put under a lot of pressure as PSG were very aggressive and pressed high up the pitch and the Barca midfield failed to control the game. Despite that PSG didn't create that many clear chances and had a lot of speculative efforts.