Moise Kean cancelled out Romain Hamouma’s opener in the first half but PSG were unable to find the net again as they let Olympique Lyonnais, who beat RC Lens 3-2, open up a three-point lead at the top of the standings.
PSG did, however, move up to second on 36 points from 18 games, leapfrogging Lille on goal difference after the northeners slumped to a 2-1 home defeat by Angers.
“It was a difficult game. We need to keep working. I’m not looking for excuses, we need to improve the way we play and to improve our performances,” said Pochettino.
“We are PSG, we must win. I arrived three days ago but I’m happy with the way the players tried to apply what we worked on during practice.”
- READ MORE
- Fernandes almost joined PSG before Man United – Tuchel
- Harry Kane made PSG's top target if Mbappe, Neymar leave
- Brilliant Mbappe scores three as PSG beat Barcelona 4-1
- Champions League is back – Who will be knocked out?
- Barca's Koeman wants protection for players like PSG's injured Neymar
- Messi PSG cover controversy: Why Man City could get advantage in transfer battle
Elsewhere, former France coach Raymond Domenech returned to the bench with Nantes, 10 years after Les Bleus were knocked out in the first round of the 2010 World Cup in embarrassing fashion, with the Canaries held to a 0-0 home draw by fourth-placed Stade Rennais.
Four days after being named as successor to Thomas Tuchel, who led the club to their first Champions League final last August, Pochettino was left contemplating the task at hand following PSG’s lacklustre performance at Geoffroy Guichard.
St Etienne took the lead in the 19th minute when Hamouma fired home after Idrissa Gueye had been dispossessed in front of the area.
Kean equalised three minutes later with a shot on the turn after a clever deflection by Marco Verratti from Kylian Mbappe’s cross.
PSG enjoyed nearly 70% of possession, but in the absence of Neymar, still recovering from an ankle injury, lacked stamina and inspiration while Mbappe had yet another match to forget.
Verratti, positioned high up on the pitch as a playmaker, was decisive for PSG’s goal but the Italy midfielder was otherwise as uninspired as the rest of the team in a disappointing performance by the French champions.
St Etienne, who are 14th on 19 points, went close to bagging all three points 20 minutes from time when Denis Bouanga’s header hit the crossbar.
Lyon were kept on their toes until the final whistle despite opening up a 3-0 lead against RC Lens courtesy of a Memphis Depay double and a Steven Fortes own goal.
Lens hit back with second-half goals by Florian Sotoca and Cheick Doucoure but came up just short and the promoted side are eighth on 27 points.
Sixth-placed AS Monaco made up for defensive blunders with a scintillating attacking display in a 5-2 victory at Lorient.