Neither Marseille nor Lyon were able to take full advantage of Paris St Germain losing 3-2 at Bordeaux as they cancelled each other out in a tense goalless draw at the Stade Velodrome.
The stalemate gives Hubert Fournier's Lyon a two-point lead over PSG at the top of the Ligue 1 standings, but they might be relieved to escape with a draw after a Lucas Ocampos effort was controversially ruled out late on for the hosts.
Third-placed Marseille, who had Jeremy Morel sent off late on, thought they had opened the scoring with eight minutes remaining as substitute Ocampos looked to have flicked home at the far post and wheeled away in celebration.
But referee Benoit Bastien ignored the claims, instead judging that scrambling Lyon keeper Anthony Lopes managed to prevent the ball creeping over the line, with TV replays proving inconclusive.
The draw leaves L'OM four points behind Lyon and two behind PSG as the title race begins to hot up.
With so much at stake, both sides began brightly and could easily have had a goal a piece inside the opening 10 minutes.
Firstly, Andre-Pierre Gignac worked Lopes when he cut in from the right to beat Samuel Umtiti but the Portugal keeper saved well with his feet before Steve Mandanda did superbly well to prevent Alexandre Lacazette at the other end after the in-form striker burst through on goal from Jordan Ferri's pass.
Marseille went close again with 13 minutes on the clock but, after Gignac cut the ball back into his path, Benjamin Mendy shot straight at Lopes.
Marseille continued to work Lopes and he had his biggest test just before the half-hour mark when Mendy's delivery found Gignac, but his header was expertly turned around the post by the Lyon keeper just as the ball seemed likely to nestle in the bottom corner.
The early high tempo dwindled as the game slipped into a lull either side of half time, with a long-range effort from Dimitri Payet, which Lopes gathered with ease, as close as either side went opening the scoring before the hour mark.
Marcelo Bielsa threw on Monaco loanee Ocampos in an effort to improve his side's impetus and the young Argentine was inches away from making an immediate impact when he just failed to get on the end of Andre Ayew's flick-on.
Lyon responded and should have scored but Lacazette fired straight at Mandanda from six yards after meeting Nabil Fekir's teasing free-kick before L'OM went even closer.
Untiti's lapse defending gifted Gignac possession and, after holding off a Henri Bedimo challenge, he fired an effort beyond Lopes but the upright came to Lyon's rescue as Ayew was unable to get close to the rebound.
The game sprung back into life inside the final 10 minutes when Ocampos appeared to bundle the ball over the line from a corner but, after wheeling away in celebration, referee Bastien waved play-on.
Then, just two minutes later, Bastien had more work to do after Morel cynically hauled down Maxime Gonalons, leaving the referee with little choice but to show the experienced defender a straight red as tempers began to flare on the pitch and in the stands.
Ten-man Marseille rode their luck late on, with Mandanda's heroics preventing Corentin Tolisso's effort from creeping in the bottom corner before the Lyon defender saw a header well saved deep into stoppage-time.
