Montpellier's advantage at the Top 14 summit was cut to four points as Racing 92 fought back to win 28-22 at home to Stade Francais on Saturday.
The leaders travel to fourth-placed Toulouse on Sunday and they will have been relieved to see Toulon, in third, claim only one point as they subsided to a shock 29-26 defeat at struggling Oyonnax.
Racing benefited from Stade's Zurab Zhvania picking up a yellow card inside 11 minutes for a dangerous tackle on Dan Carter, and they soon capitalised as Boris Palu went over.
Carter converted but Racing found themselves 14-7 down at the break as Stade hit back through Jimmy Yobo and Marvin O'Connor.
The hosts came out firing after the interval, however, and were back in front by the hour mark courtesy of Teddy Thomas' brace - the second on the back of an excellent break from Virimi Vakatawa.
Marc Andreu's score 10 minutes from time effectively put the game beyond Stade, for whom Morne Steyn's penalty and Baptiste Lafond's interception try in the last minute set up the chance to secure a losing bonus point, only for Steyn to miss the extras.
A maximum return for Toulon would have seen them join Racing in closing to within four of Montpellier, but Fabien Galthie's men were put to the sword by the boot of Ben Botica.
The New Zealander kicked 19 points, including converting tries scored by Rory Grice and Steven Sykes - the latter going over with a minute to go to snatch victory from the jaws of defeat for Oyonnax, who remain in the bottom two but have now won four in a row.
Meanwhile, Clermont Auvergne thrashed Pau 38-14, La Rochelle edged out Lyon 19-15 and Bordeaux-Begles came away 15-10 winners from a trip to Agen.
