Michy Batshuayi scored a second-half double, with his first coming 39 seconds after being brought on for Andre-Pierre Gignac at half-time, while Alaixys Romao and Andre Ayew also found the net.
Victory at the Stade de France sees Marseille stay within two points of leaders and arch rivals Paris Saint-Germain ahead of Le Classique at the Stade Velodrome on April 5, and move a point behind Lyon after they succumbed to a 2-1 home defeat to Nice.
"The first half of the first half was positive," Bielsa said. "Then we lost influence in the game. In the second half, the quick goal [from Batshuayi] greatly facilitated our game. The spaces were opened and we were offered more opportunities."
Marseille have scored 10 goals in their last two away games, having thumped Toulouse 6-1 on the road two weeks ago.
"In these two games we let our opponents create more opportunities than we imagined," Bielsa added. "These two results are exaggerated, but this team has grown because it needs from fewer opportunities of goal to score.
"The remaining days are going to be decisive, but especially the match against PSG, which is a classic."
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