Racing 92 paid the price for resting Dan Carter and other stars as the front-runners were thrashed in the French Top 14.
Jake White's Montpellier outfit ran in nine tries for a 60-7 win that elevated them to fourth on the table and left Racing's top position vulnerable.
Racing took a gamble as they eye the looming crunch European Champions Cup quarter-final against holders Toulon, resting several big names.
Carter was absent from the playmaker's role and Welsh halfback Mike Phillips was also rested along with Argentine speedster Juan Imhoff. Former All Blacks wing Joe Rokocoko was on the bench while six French internationals were also missing through Six Natrons duties.
The result was a massacre at Montpellier's Altrad Stadium.
Elsewhere, struggling defending champions Stade Francais snapped a run of three successive losses with a 33-20 win at home against play-off hopefuls La Rochelle.
Across in England, five penalties from the boot of Kiwi Ben Botica wer enough to save Harlequins who lost 21-15 to Worcester in their Premiership match in London.
Harlequins missed the chance to climb into the top four while Worcester's third win in a row looks certain to save them from relegation.
Controversy surrounded captain GJ Van Velze's try just before halftime when an assistant referee appeared to raise his flag on the halfway line for a Worcester lineout.
Several players stood still and waited for the whistle, but Van Velze took advantage to scoop up the loos ball and run clear for the try that was confirmed by referee Craig Maxwell-Keys