PSG were 3-2 winners at Metz after Ezequiel Lavezzi poked home the match-winner from close range with 10 minutes remaining.
The reigning French champions, who went to the summit provisionally, were forced to survive an almighty scare at the Stade Saint-Symphorien.
Zlatan Ibrahimovic's return to the starting line-up saw the visitors race out to a two-goal before the 16-minute mark thanks to Javier Pastore and a Gaetan Bussmann own goal.
Mets responded in the second half, however, Modibo Maiga - on loan from West Ham United - converting two penalties in the space of four minutes shortly after the break, though Lavezzi eventually came to PSG's rescue late on.
"I was confident even after the equaliser. I thought we would win 3-2," Blanc told reporters post-game.
"Our first period was very well controlled against a team of Metz who feared us a lot.
"We can think at half-time the game is pretty easy. But after the first penalty, Metz enters the game and then we had a difficult time.
"Paris had the means to win the game before the third goal. We have seen players who have given the means to get the win. There are still some flaws but the main fact is taking three points."
