Toulouse head coach Ugo Mola said his side were "ordinary" after the French Top 14 leaders lost at home to strugglers Montpellier 29-16 on Saturday.
English fly-half Alex Lozowski, on loan from Saracens, kicked 16 points for the visitors at Stade Ernest-Wallon to help billionaire-backed Montpellier move nine points clear of the relegation play-off.
Toulouse, the record 20-time champions, without the likes of Antoine Dupont and Romain Ntamack on France Six Nations duty, lost for just a second time since November. They are three points clear of La Rochelle, who claimed a first win at Bordeaux-Begles since 2015.
"Montpellier's quality caused us a lot of problems today. When we don't play with speed we become an ordinary team," Mola said.
"Tonight we were a very, very ordinary team. A night to forget," he added.
South Africa's Johan Goosen made just his second appearance of the campaign in an injury-ravaged season while fellow Springbok Cheslin Kolbe started at full-back for the home side.
Lozowski slotted two penalties and a conversion with as No. 8 Alex Becognee crossed and the visitors led 16-6 at the break.
The 27-year-old added eight further points in the second half with Jan Serfontein scoring as they held on despite Matthis Lebel's try for the hosts with 17 minutes to play.
- Victim Matsushima -
Earlier, Clermont captain Morgan Parra said Kotaro Matsushima was "fine" after the Japan full-back was the victim of challenges that drew yellow and red cards in a 34-27 win at Stade Francais.
Matsushima passed to Alivereti Raka for a first half score and, late in the game, was on the wrong end of a dangerous tackle from Jonathan Danty that brought a sin bin and then a high boot from winger Lester Etien, who was sent off.
"Kotaro is fine. It's the law. Etien jumps, firstly his foot is loose then he stiffens it," Clermont captain Morgan Parra said.
"It's a job well done for us against a direct opponent for the play offs. It's very good," he added.
La Rochelle's double World Cup winner Victor Vito celebrated his 34th birthday with a 26-11 victory at Bordeaux-Begles.
South Africa winger Dillyn Leyds scored one of visiting La Rochelle's three tries at Stade Chaban Delmas and former New Zealand Maori fly-half Ihaia West kicked 11 points.
Vito's outfit moved four points clear of Racing 92 who are third, outside an automatic semi-final spot.
Argentina winger Juan Imhoff made his 200th appearance for the Parisians in a 23-13 loss at lowly Bayonne.
In the final game of the day, the Springboks' World Cup winner Eben Etzebeth starts at blindside as Toulon head to Lyon.
Fly-half Louis Carbonel comes into the run-on side for the away team after being an unused reserve 24 hours later in France's loss to Scotland.