New Zealander Ben Botica kicked 12 points to send Castres to third place in the French Top 14 in Saturday's 15-9 home win over Stade Francais.
Botica's efforts extended the five-time champions' winning home league record to 16 games, a run which stretches back to December 2020.
Ex-New Zealand centre Ngani Laumape started for the Parisians but was unable to inspire a late comeback in heavy rain.
"It was difficult, we faced a very good Stade Francais team in difficult weather conditions," Castres captain Gaetan Barlot told Canal+.
"The points from the boot made the difference. We're winning difficult games, we have to keep this positive cycle," he added.
After five games over the past two weekends were postponed due to Covid-19 cases, two matches this weekend were put on hold for the same reason.
South Africa's Cheslin Kolbe will have to wait for his Toulon Top 14 debut as they were scheduled to host La Rochelle while champions Toulouse were set to welcome Montpellier on Sunday.
The five fixtures going ahead were the final games to be played before players could be blocked from featuring after January 15 if the French upper house of Parliament passes a bill requiring a full course of vaccination to enjoy basic parts of life, such as entering sporting stadia.
According to the president of second-tier Bayonne, Philippe Tayeb, around 20 squad members in France's top two divisions would be unable to play.
Stade Pierre-Fabre had just 5,000 fans present, of its 12,500 capacity, with new limits in force in France on spectators at outdoor and indoor events.
The hosts led 6-3 at the break after a turgid affair in heavy conditions as full-back Julien Dumora added to Botica's early penalty.
Joris Segonds kicked the Parisians only points of the half.
Botica, 32, the son of former dual-code New Zealand international Fran Botica, slotted three further penalties to make it 15-6 quarter of an hour after the interval.
Stade Francais had two attacking scrums in the final two minutes as the hosts' half-back Rory Kockott was shown a late yellow card but the 14-time winners were unable to claim victory and end the home side's impressive run on their own turf.
- Tuisova off the mark -
Later, league leaders Bordeaux-Begles edged struggling Brive 22-19 despite trailing by 11 points at the interval.
Fiji Olympic champion Josua Tuisova opened his account for the season thanks to former All Blacks fly-half Lima Sopoaga's maiden assist of the campaign as Lyon cruised past Pau 35-10.
In a repeat of last season's second-tier promotion final, Perpignan moved up to 11th place with a 25-23 win at Biarritz thanks to France full-back Melvyn Jaminet's late penalty.
The Catalans' success in the Basque Country leaves Kolbe's three-time European champions just outside the relegation zone on their head-to-head record with 13th placed Brive.
In the final game of the day, and the weekend, Racing 92 ended their four-game streak without a Top 14 victory, their worst run of league defeats since 2012.
They overcame Clermont 33-28 in front of just 2,000 supporters due to the Parisians' ground being an indoor arena, to claim a first domestic victory since October.
Next weekend, Top 14 clubs are set to feature in European competitions after tournament organisers said on Friday the games would go ahead despite strict travel rules in place between France and Britain.