PSG moved to within a point of Marseille at the summit thanks to goals from Brazilian Lucas Moura and Uruguay striker Edinson Cavani at the Parc des Princes.
The defending French champions - unbeaten in the league so far - weathered Marseille's early pressure and took a 38th-minute lead through Moura, who netted the ball past visiting goalkeeper Steve Mandanda.
Giannelli Imbula saw red with 12 minutes remaining, ending Marseille's hopes of salvaging anything from the clash, as Cavani struck five minutes from time to seal victory for PSG.
Afterwards, Blanc said Moura's opener gave PSG the belief they could beat Marseille.
"It is a great satisfaction. It was a very good game because there were two very good teams, beautiful players who wanted to produce the game," Blanc said.
"Marseille were better for the first 25 minutes, including physically and duels they were fresher than us.
"It made us aware that it was necessary to raise our game and take more risks.
"We then realised that if we maintained this level of play, you could win the game. Marseille has created some dangerous chances, too.
"The opening goal was decisive: it has us pumped up their morale and it has definitely affected.
"In the second half we were superior. We play 11 against 10, it's still easier. But overall, the victory is deserved."