In a match full of drama and controversy, Saint-Etienne threw away a 2-0 second half lead albeit hindered by a red card which allowed Laurent Blanc's men back in the match.
The point allowed PSG to cling to top spot as they lead Monaco on goal difference after Claudio Ranieri's side defeated Lyon 2-1 earlier in the day.
"It was a difficult evening for Paris and an intense match but I enjoyed myself regardless," Blanc said.
"PSG have to understand that we are going to come up against very good, organised teams and we were in a great stadium tonight.
"We gave them two goals which were terrible defensive mistakes and we were punished.
"I thought we were average and Saint-Etienne fully deserved at least a point." added the former France and Bordeaux handler.
Midfielder Benjamin Corgnet opened the scoring after just 18 minutes when he took advantage of a missed clearance from Brazilian centre-back Marquinhos to crash the ball past a static Salvatore Sirigu in the PSG goal.
The visitors failed to convert their possession dominance as they chased an equaliser and fell further behind in comical circumstances six minutes after the break.
Sirigu came out of his goal to collect a cross but tangled with his own defender Alex which allowed Romain Hamouma to clip the ball into an empty goal.
It was the first time since last March that PSG had conceded two goals in a league match -- ironically against the same opposition.
But the turning point occurred on 59 minutes when Fabien Lemoine tangled with Ezequiel Lavezzi who elbowed him in the face leaving him covered in blood.
Referee Ruddy Buquet saw the incident differently and sent off the furious Frenchman who may have been dismissed for dissent in the heat of the moment.
The red card swung the momentum in favour of Blanc's men and when Edinson Cavani stabbed the ball home from close range after a good pass from Brazilian defender Maxwell, the comeback was half completed.
However, stubborn defending from Saint-Etienne and some rousing support almost inspired Christophe Galtier's League Cup holders to victory.
But with seconds remaining a looping ball into the penalty area from Matuidi eluded Saint-Etienne 'keeper Stephane Ruffier and bounced into the net.
Earlier at the Louis II stadium, Ligue 1's top scorer Radamel Falcao found the target for the first time in four matches as he helped Monaco defeat Lyon 2-1.
The former Atletico Madrid striker chipped Lyon 'keeper Anthony Lopes in the 36th minute following Mounir Obbadi's 28th minute opener as Claudio Ranieri's men extended their unbeaten run to seven wins and four draws in 11 outings.
French striker Bafetimbi Gomis gave the visitors hope with 28 minutes left when he powered home a close-range header but it wasn't enough as Lyon suffered their fifth defeat.
"It was important for Falcao to score and when he scores Monaco usually win and we have to win all our matches if we want to stay at the top," explained Monaco's Portuguese defender Ricardo Carvalho.
Lille slip to third, two points back behind PSG and Monaco following their disciplined 1-0 win at Nantes on Friday.
Earlier on Sunday, Bordeaux rode two late goals from Mali international Cheikh Diabate and Polish winger Ludovic Obraniak to defeat Montpellier 2-0 in a battle of former champions at the Chaban Delmas stadium.