The reigning champions had the chance to take first place from Lille on goal difference but strikes from Randal Kolo and Moses Simon wiped out PSG’s half-time lead, which came through Julian Draxler, and inflicted a fourth home defeat this campaign on the capital club.
Lille stay top and gain a point on PSG, taking their lead to three on both them and Lyon, who could only draw at Reims on Friday.
Nantes move out of the automatic relegation places with just their fifth win of a troubled season, a point from safety.
PSG coach Mauricio Pochettino made five changes from the team that got past Barcelona and into the Champions League quarter-finals midweek, and his side could easily have been ahead early on.
Angel Di Maria’s 11th minute rocket was well-saved by Alban Lafont and shortly afterwards Marquinhos should have done better when he headed over Draxler’s corner when completely unmarked.
However Nantes came into the game after that and thought they should have been given a penalty in the 20th minute when Presnel Kimpembe brought down Randal Kolo, only for the spot-kick not to be awarded.
Ten minutes later home goalkeeper Kaylor Navas kept the scores level with a fabulous save from Ludovic Blas’ well-hit half-volley, and after that PSG briefly woke up.
First Kylian Mbappe worked some space for a tame shot, before Rafinha tested Lafont’s fingers with a stinging effort from the edge of the box.
Draxler then opened the scoring three minutes before the break when he pounced on a loose ball to lash a left-footed shot past Lafont.
However Nantes levelled in the 59th minute amid some confusion among the PSG camp on the sidelines which eventually led to Di Maria being substituted — with Pochettino following the Argentine down the tunnel — as Kolo collected a wayward Mbappe pass before ramming home his finish.
– PSG lose their way -PSG seemed to completely lose their way and Nantes took full advantage in the 71st minute through Moses Simon, who tapped home Kolo’s square pass and then had to endure a long wait while VAR made sure no-one was offside in the build-up.
Former PSG player and coach Antoine Kombouare then watched his new team hold out bravely as the hosts tried in vain to get something from the game.
Christophe Galtier’s Lille stay in first place after their largely uneventful draw at Monaco.
Monaco remain seven points behind Lille in fourth after failing to pick up ground in the race for next season’s Champions League.
They stay four points behind third-placed Lyon, who occupy the last Champions League spot.
Monaco, who had a Wissam Ben Yedder goal ruled out for offside following a VAR check in the first half, almost snatched the points at the death through substitute Stevan Jovetic but the Montenegrin’s close-range effort was well kept out by Mike Maignan.
“Jovetic is very disappointed. It was a big opportunity but Maignan is excellent,” said coach Nico Kovac.
“I’m satisfied with how my team played… My impression is that Lille came here to get a draw, as they played on the counter.”
The draw in the Principality also extended to 11 matches an unbeaten league run for Lille that stretches back to early January.
Next weekend PSG travel to Lyon, themselves also three points off the lead while Lille host relegation-threatened Nimes.