The Ligue 1 big-spenders took full advantage of a horror show from Guaita to secure two priceless away goals, but Rami provided the hosts with a late lifeline
A nightmare display from goalkeeper Guaita saw the hosts concede two eminently preventable goals from Ezequiel Lavezzi and Javier Pastore in the first half as Ernesto Valverde's side, despite seeing the majority of the ball, failed to make many significant inroads in the attacking third.
PSG took further control of the game in the second half and in truth, should have won by a much larger margin after spurning a hatful of chances, and its profligacy would come back to haunt the French club as Adil Rami converted a potentially priceless stoppage-time goal.
And the Ligue 1 outfit would end the game in a complete shambles, as Zlatan Ibrahimovic saw an even later red card for a reckless challenge, ruling him out of a now finely poised second leg in Paris in three weeks.
Valverde fielded Jonas from the start on the left flank while for the visitors, Mamadou Sakho deputized for the injured Thiago Silva in defense, with January signing Lucas Moura making his Champions League debut ahead of Jeremy Menez.
PSG was unlucky not to be ahead nine minutes in when Lucas Moura cracked a long-range effort off the inside of the post. But with its next attack, the Ligue 1 side would take the lead through a goal that owed as much to Lavezzi’s brilliance as it did to Guaita’s blunder.
The Argentine did fantastically play a one-two with Pastore and dribble past Ricardo Costa, but his shot from the right side, though powerful, should have been met by Guaita, instead of flying straight through his hands.
PSG was certainly the better side throughout the first half as Valencia, despite holding the majority of possession, could not make it count in the attacking third as it failed to seriously test Salvatore Sirigu.
Guaita was a bundle of nerves in the hosts’ goal, and did not look comfortable handling a curled effort from Lavezzi with 38 minutes gone. And moments before halftime, the Valencia keeper embarrassed himself with another howler.
Lucas beast Andres Guardado expertly on the flanks and cut back to Pastore at the top of the box. Again, Guaita should have at least made contact, but instead let the ball ricochet through his legs and into the back of the net.
The chances continued to fall PSG’s way in the second half. Guaita’s poor parry saw Lavezzi miss from point blank range, before the Argentine again fluffed his lines from in close, firing straight into the Valencia keeper’s arms from Marco Veratti’s feed.
Ibrahimovic narrowly missed poking home a one-two with Lavezzi, and Clement Chantome had a goal ruled out for offside before finally, with the game entering its closing stages, Valencia managed its best chance.
Tino Costa’s diagonal ball picked out Nelson Valdez in the area, who did well to evade the attention of Alex, but blasted into the side netting from a position where he really should have hit the target.
But just when all seemed lost, Valencia surged back into the tie as Rami struck from Costa's free kick in injury time before, with one of the last kicks of the match, Ibrahimovic was given his marching orders for a poor challenge on Guardado, leaving all to play for in the second leg.