Diego Rolan settled a thrilling contest two minutes from time as PSG lost for the first time in 16 matches across all competitions on the back of their memorable midweek fightback to dump Chelsea out of the UEFA Champions League.
Zlatan Ibrahimovic was sent off at Stamford Bridge but scored twice on Sunday, first pegging back Ludovic Sane's opener five minutes after the restart.
Wahbi Khazri nodded home at the back post in the 70th minute, although Ibrahimovic appeared to have salvaged a point from the penalty spot with five minutes to play.
But there was a further twist as Mariano made amends for conceding the spot-kick by crossing for Rolan to steal the points.
Ibrahimovic courted controversy once more after full-time, with the French Football Federation likely to investigate a foul-mouthed rant against the match officials in the mixed media zone after the match.
Lyon hold a slender two-point advantage at the top of the table after playing out a goalless draw at Marseille.
The home side held on for a share of the spoils despite having Jeremy Morel sent off in the 85th minute.
Earlier on Sunday, Belgium international Divock Origi fired a hat-trick as Lille eased to a 3-0 victory over Rennes.
Origi ended a sixth-month scoring drought in emphatic fashion by taking home the matchball.
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