OM, who have lost only once in their last seven league outings after a terrible start to the season, salvaged a point at the Velodrome, twice coming from behind through Remy Cabella and Bouna Sarr to answer Casimir Ninga's double for Montpellier.
Marseille are ninth with 23 points, a massive 22 points behind runaway leaders Paris St Germain but now only six points adrift of third-placed Caen.
Ninga opened the scoring from close range after being set up by Ryad Boudebouz in the 32nd minute, only for Cabella to equalise three minutes into the second half.
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Eight minutes later, Chad striker Ninga beat Steve Mandanda again after taking advantage of a blunder by Karim Rekik.
In the 72nd minute,though, Barr latched onto Georges-Kevin Nkoudou's cross to make it 2-2.
(Reporting by Julien Pretot; Editing by Ian Chadband)
