Bordeaux-Begles hammer Toulouse in Dupont absence
Scrum-half Maxime Lucu scored 17 points for the home side, who moved up to fourth in the table, two points off second-placed Montpellier in the final automatic semi-final berth.
Toulouse remain top of the table despite their first league loss since January and are 10 points clear before hosting Montpellier next weekend with Dupont expected to return.
The game was billed as the battle between France's two leading fly-halves as Matthieu Jalibert welcomed rival Romain Ntamack to the Stade Atlantique.
Jalibert started four of Les Bleus' five Six Nations games as Ntamack had been sidelined since late December.
"Like every time we play Toulouse, they are open affairs," Jalibert told Canal+ after the re-run of the past two Top 14 finals.
"By turning the screw little by little we found opportunities.
"We claimed five points so it's good for the rest of the season," he added.
The visitors chose to rest a handful of their France Six Nations champions, including former World Rugby player of the year Dupont and full-back Thomas Ramos, who kicked the last-gasp winning penalty against England a week ago.
The returning Ntamack had the better of the first 35 minutes as his 13 points, including a try gave his side a 13-10 lead.
But it was Jalibert's outfit, Champions Cup winners in May, who had a two-point advantage at the break thanks to the playmaker's assist as he set up winger Madosh Tambwe.
After the interval, Ntamack had a second try denied after a check by the video referee before the hosts took control of the game.
By the hour mark, Yannick Bru's home side led 30-13 as centre Damian Penaud, dropped from France's Six Nations squad before the tournament, and Lucu scored, inspired by a Jalibert interception.
With a quarter of an hour left, Ntamack was replaced on his first appearance in almost three months before late tries from replacements Arthur Retiere and Xan Mousques for Bru's outfit and France centre Kalvin Gourgues crossed in additional time for Toulouse.
On Saturday, Australia full-back Tom Banks scored as Montpellier won 20-17 at Clermont to go second.
Toulon head coach Pierre Mignoni returned as they lost 46-27 to Stade Francais, having taken almost a month off due to mental health problems.
Pau missed out on the chance to go above Montpellier as they suffered a 20-6 loss at La Rochelle.