Paris - Double World Cup winner Victor Vito crossed for a brace of tries as Top 14 leaders La Rochelle withstood a fighting comeback from Montpellier on Sunday to guarantee they finish first in the regulation season.
Montpellier's giant Fijian winger Nemani Nadolo had a try ruled out by the television match official in extra-time in a nail-biting match which sees La Rochelle now on 84 points, with just one match left before the play-offs.
A losing bonus point for Montpellier sees the southern club in third on 72 points, two behind Clermont, who occupy the second automatic semi-final spot. Toulon lie fourth (65), two ahead of Castres (63).
Pau (57) occupy the sixth play-off spot, but that will likely change after Sunday's late game between Parisian rivals Stade Francais and Racing 92.
Willem du Plessis, with three South African namesakes also on Montpellier's team sheet, opened the scoring when he crashed over for a try he also converted.
La Rochelle's Australian flyhalf Brock James and Du Plessis exchanged penalties shortly after in what would be a fine kicking display in rainy conditions by the two players.
La Rochelle, who lost to Gloucester in the semi-finals of the European Challenge Cup last weekend, looked to have wrapped the game with tries from Vito, ubiquitous hooker Jeremie Maurouard and Pierre Aguillon.
But at 40-16 up after 64 minutes, they hadn't counted on a ferocious comeback from the visitors, who scored three tries (penalty, Nadolo and Duhan van der Merwe) in the final six minutes after the sin binning of James for pulling down a maul.
Then came the anxious wait as Nadolo crossed the whitewash before referee Romain Poite whistled the end of the game to the huge relief of La Rochelle, who finish the regular season unbeaten at home.