The midfielder came off the bench to score in the game's penultimate minute to secure a 1-0 victory after a lackluster performance against opponents reduced to 10 men.
Despite a lackluster display, Laurent Blanc's men grabbed victory at the death when Lucas Moura's fine through pass picked out the substitute, who shot through Jesper Hansen's legs.
By this stage Kassim Abdallah had been sent off, but Evian had displayed plenty of guts throughout, particularly in the opening period, when Daniel Wass' free kick left the crossbar shaking.
Blanc's side now hold a 10-point lead over second-placed Monaco with four games remaining, and will be assured of a second consecutive title with victory over Sochaux on Sunday - although it would be crowned champion sooner should Monaco lose at Ajaccio on Saturday.
Evian, meanwhile, remains five points above the relegation zone.
PSG typically looked to control possession from the whistle, but it was the visitors that almost opened the scoring in the fifth minute when Wass' 30-yard free kick crashed against the bar.
The game's next chance also fell to Wass, the Denmark international rising highest to head Cedric Barbosa's corner toward goal only to be denied by Salvatore Sirigu's fine save.
Having survived those scares, the hosts created their first meaningful opportunity on 22 minutes.
Marco Verratti pinched the ball deep in Evian's half before slipping a neat through ball into the path of Ezequiel Lavezzi, only for the Argentine forward to be denied by the quick thinking of Evian keeper Hansen, who saved with his foot.
Adrien Rabiot then flashed an effort over the bar from the edge of the box, but PSG remained frustrated in its hunt for the opener.
The home side upped the tempo after the break, and Lavezzi really should have broken the deadlock after 58 minutes.
Javier Pastore's cute pass into the box was met by Rabiot, who in turn laid a teasing ball across goal from the left to the former Napoli man, who side-footed wide of the far post from six yards.
Evian was dealt a blow on the hour mark as Abdallah - who had only been booked five minutes earlier - was sent off for a second bookable offense for chopping down Lucas Digne.
PSG then began to control proceedings and Lavezzi's dipping effort from 30 yards was tipped over by Hansen.
Blanc's side wasted a golden opportunity with 10 minutes left as the ball fell kindly to Matuidi near the penalty spot, but he flashed wide.
However, the France international made amends shortly after as he collected fellow substitute Lucas' through ball and sent the home fans into delirium.