The Uruguayan, a big-money buy from Napoli, blasted home four minutes from the end to ensure the capital club a 1-1 draw.
Benoit Pedretti had given Ajaccio an early lead when he bent in a 20-yarder and despite PSG's dominance, the Parc des Princes crowd had to wait until the end for their latest major arrival to prove his worth.
The point nonetheless leaves new boss Laurent Blanc waiting for his first league win in charge after PSG were held to a 1-1 draw by Montpellier on the opening day.
While PSG have endured a tough start, newly-promoted Monaco continued their successful start to life back in the top flight with a 4-1 win over 10-man Montpellier.
Emmanuel Riviere's first career hat-trick sealed victory after Radamel Falcao opened the scoring from the penalty spot early in the first half.
Claudio Ranieri's men were pegged back by a Victor Montano effort before Riviere took over.
Lorient picked up their first points of the new season after recovering from a goal down to defeat Nantes 2-1 at Stade Du Moustoir.
Newly-promoted Nantes defeated Bastia 2-0 in their opening match and were on course for another successful outing after taking a 17th-minute lead through Olivier Veigneau.
However, they were left empty-handed as Lorient drew level before the break thanks to Vincent Aboubakar and then snatched a 61st-minute winner through Jeremie Aliadiere's unstoppable free-kick.