PSG opened up a commanding lead at the summit of the French top flight by completing a league double over their arch rivals with a confident performance at the Parc des Princes on Sunday.
Maxwell opened the scoring for PSG early in the second half, before Edinson Cavani marked his return from injury with a goal that sealed the points 11 minutes from time.
The victory puts the capital club in pole position to retain the title following Monaco's loss at Saint-Etienne on Saturday, but coach Blanc is refusing to get complacent.
"Nothing is decided in our minds until it is mathematically proven," Blanc told Canal +.
Marseille showed plenty of industry but struggled to create chances in a game dominated by the defending champions from start to finish.
And Blanc was quick to highlight the hosts' command of possession as the reason for their victory.
'I thought it was good that Marseille brought their own game to us," Blanc added. "They played their own way.
"As is often the case it was possession that made the difference. We forced them to defend and did not allow them the ball."
Meanwhile, Blanc's Marseille counterpart Jose Anigo felt Maxwell's opener effectively ended his team's hopes of getting anything from the game.
"In the first half there was not a world between the two teams," he said. "After the first goal it becomes difficult. They (PSG) had too much talent.
"We are disappointed but not disheartened by this match. We showed fight."
