Paris - La Rochelle kept pace with the Top 14 leaders with a workmanlike 16-9 victory over Racing 92 on Sunday in a dire encounter.
Last year's surprise regular-season table-toppers have carved out a reputation for being tough to topple and they were at their stubborn best in frustrating the 2016 champions.
The win took La Rochelle up to third, just five points behind this year's surprise package, Lyon, after a fifth win in seven matches.
Racing remained in the bottom half after a lacklustre display in which they failed to even snare a losing bonus.
La Rochelle's success was built on forward power with a much-changed Racing pack unable to contain them.
Maxime Machenaud, playing at flyhalf rather than scrumhalf as the injured Dan Carter was missing, gave Racing an early three-point lead from the tee, but the rest of the first half belonged to the hosts.
Alexis Bales knocked over two penalties before La Rochelle launched an attack from a scrum in Racing territory.
With the backline running intelligent lines, New Zealand international No.8 Victor Vito managed to break through a gap and flip an overhead pass to replacement flyhalf Vincent Rattez to cross the whitewash, despite being tackled by Teddy Thomas.
A second Machenaud penalty just before half-time kept Racing in touch but the France international missed a relatively straightforward kick at the posts early in the second period.
Bales then kicked his third penalty following a break from France back-rower Kevin Gourdon and Fijian fullback Kini Murimurivalu.
Racing toiled for long periods deep in La Rochelle territory but lacked the guile needed to break through a disciplined and committed defence.
Machenaud did knock over a third penalty late on but it wasn't enough to snatch a losing bonus point.
Lyon went top with a bonus point 25-6 win at Agen on Saturday as previous leaders Montpellier fell to a shock 31-20 defeat at previously misfiring Stade Francais.
Later on Sunday, champions Clermont travel to record four-time European Cup winners Toulouse.