Springbok flyhalf Handre Pollard nailed over a 77th minute penalty as Montpellier beat Castres 29-10 to win their maiden French Top 14 title on Friday in a re-run of the 2018 final at the Stade de France.
The 28-year-old, who will join English Premiership outfit Leicester Tigers next season, came off the bench in the final 12 minutes, while English No. 8 Zach Mercer played a leading role in match.
Pollard is expected to be back in South Africa early next week as the Boks prepare for their three-Test series against the Wales in July.
Mercer, who joined the Mediterranean side this season from Bath, set up Arthur Vincent for Montpellier's opening try as the 2018 runners-up gained revenge for the defeat four years ago.
"It was really exceptional. We had a huge season, we really deserved that," Montpellier's Paolo Garbisi told Canal+.
"We knew with Castres that you have to surprise them with desire from the start. We knew they never give up, that's what they did.
"We managed to hold on until the end and now it's superb."
Kick-off was delayed by 19 minutes after French President Emmanuel Macron was whistled on and off the field as he was presented to the players.
Both Castres and Montpellier named the same starting XVs which won last weekend's semi-finals against record 21-time champions Toulouse and Bordeaux-Begles respectively.
Philippe Saint-Andre's Montpellier dominated from the off and they were rewarded after six minutes as winger Vincent dived over in the corner from a grubber-kick by Mercer, who is ineligible for his country as he plays abroad.
By the 13-minute mark Montpellier led 17-0 as lock Florent Vanverberghe and full-back Anthony Bouthier, who was beautifully set-up by a Vincent loop pass, added to Castres' woes, who seemed to be frozen by the pre-match build-up.
"That start to the match was catastrophic," Castres captain Mathieu Babillot told Canal+.
"We're very disappointed tonight. That's how sport goes, it's difficult, it's cruel."
Castres head coach Pierre-Henry Broncan's early worries intensified just a quarter of an hour in, as influential fly-half Benjamin Urdapilleta left the field with an ankle issue, and without a recognised stand-off on the bench, full-back Julien Dumora deputised in the No. 10 shirt.
Montpellier's retiring ex-France captain Guilhem Guirado left the field for the final time as a professional player on 27 minutes as he suffered a neck injury, and was replaced by Australia hooker Brandon Paenga-Amosa.
The score was 23-3 at the break after Dumora opened his team's account, while Benoit Paillaugue kicked two penalties for Montpellier to put the seal on an almost perfect first half.
Castres began the second 40 minutes on a positive note and were denied shortly after the interval as Mercer and Vincent held up Dumora over the line.
Montpellier, last season's European Challenge Cup winners, were then able to clear their lines as captain Yacouba Camara won a penalty at a ruck a quarter of an hour into the second half.
Castres, who finished the regular season top of the table despite only having the league's 10th highest budget, were denied a second time as replacement prop Wayan de Benedittis failed to ground with 32 minutes left.
The final quarter was a turgid affair in humid early summer conditions and Garbisi extended the advantage for the two-time runners-up with a penalty goal with 12 minutes remaining.
Castres scored a consolation try as Vilimoni Botitu glided over with four minutes to go but it failed to dampen the Montpellier fans' long-awaited celebrations.