Lyon consigned Toulouse to a home defeat last weekend, but Ugo Mola's side put that behind them to move just five points behind Montpellier.
There was nothing to choose between the two title contenders in the first half at Stade Ernest Wallon, where Nemani Nadolo barged his way over from close range before Yoann Maestri's converted try made it 7-7 at the break.
Francois Cros went over from the back of a scrum as Montpellier failed to withstand the pressure and a Thomas Ramos penalty gave the home side an eight-point advantage.