Diarra, formerly of Bayern Munich and now with Bastia, is a member of the French under-21 side and played for them as recently as November making him ineligible to play for Mali.
The visitors' winning goal came in the 50th minute from Argentine Javier Pastore and allows PSG to wrap up the title on Sunday if they record a better result against Valenciennes than second-placed Marseille manage in Saturday's match with Bastia.