Top 14 leaders La Rochelle sealed a play-off place and moved 11 points clear with a 23-13 win at Pau after Racing 92 beat second-placed Clermont Auvergne.
La Rochelle are assured of a top-six finish after claiming their 15th top-flight win of the season, with Brock James scoring 18 points to seal their latest success.
Australian fly-half James went over for the opening try just eight minutes in and converted before adding two penalties following Watisoni Votu's score for the home side.
La Rochelle took a slender 13-10 lead into half-time, but Pau were level when Tom Taylor slotted over his second penalty of the afternoon.
James put La Rochelle back in front from the tee and Afa Amosa powered his way over for a second La Rochelle try, which James converted as the leaders ground out yet another win.
Clermont have now lost three of their last four matches after going down 27-24 at Racing despite a spirited display with 14 men for the last 20 minutes.
Racing boosted their chances of making the play-offs with a tense victory in their first game since plans for a merger with Stade Francais were announced and quickly scrapped following a hostile reaction to the plans from players and supporters.
The champions stormed into a 20-0 lead at the interval courtesy of a try in the first minute from Leone Nakarawa, another from Chris Masoe and 10 points from the trusty boot of Dan Carter.
Clermont looked to be out of it when Benson Stanley was shown a second yellow card for tackling Brice Dulin without the ball and Juan Imhoff scored a third Racing try soon after.
But Clermont made a great fist of it, forcing a penalty try and scoring another through Alivereti Raka with Maxime Machenaud in the sin bin, but they ran out of time to avoid defeat.
David Mele scored all of struggling Grenoble's points, including a late drop goal, in a 21-20 win over fifth-placed Castres, while Lyon hammered bottom side Bayonne 52-7 and Bordeaux Begles edged out Toulouse 20-11.