A 20th-minute goal from Serge Gakpe saw Nantes upset Marseille 1-0 at the Stade de la Beaujoire-Louis Fonteneau.
Bielsa's men are fourth and seven points adrift of league leaders Lyon, with their spot in the European places suddenly under threat.
The Argentine took responsibility for his team's loss, and said their title bid was over.
"A team that loses three consecutive matches in the closing stages of the championship cannot hope to win the title," Bielsa said.
"Our play as a team wasn't good enough and it is purely the coach's responsibility.We played poorly on an individual level too. We could have won but we played negatively and without fluency.
"We could have avoided the way they upset our equilibrium and also missed chances to equalise at the end."
Marseille have suffered losses to Paris Saint-Germain, Bordeaux and Nantes after appearing a huge chance of winning their first league title since 2009-10.
Bielsa said his team had let opportunities slip in the title race.
"We are clearly in a negative dynamic. This is the third time we have the opportunity to get back into the championship," he said.
"After Lens and Lyon [a win and a draw in March], which were two very good games, we had the opportunity to move up the rankings, but we have not succeeded."
