Clermont set a club record with a 10th successive win in the French Top 14.
Springbok captain John Smit played tighthead prop for 65 minutes as Clermont hammered Auch 36-15 away from home to retain top spot ahead of Toulouse.
Smit, who has played mostly at hooker this season, told Keo.co.za he was pretty buggered after the tighthead effort, but that playing there could only improve his all-round game.
Springbok centre Marius Joubert, according to reports, again excelled and has easily been the form centre in the competition.
Smit, who was named Bok captain a couple of months ago, may miss the French Top 14 play-offs because of international commitments against Wales in June.
Perpignan consolidated their top four place with an away win against Brive. Percy Montgomery kicked a conversion and two penalties and former Stormers centre Gavin Hume added a drop goal in the 16-7 victory.