Montpellier, with six academy players in their starting XV, stunned Worcester 22-17 in the Amlin Challenge Cup on Thursday at Sixways.
The French came to play and Worcester appeared to have taken them lightly, conceding far too many penalties in the first half and enabling the tenacious youngsters to build up a 15-3 lead.
But a try right on half-time from a driven line-out by Pat Sanderson put Worcester back in the game.
Then in the second half, just as Worcester looked to be getting back into the game, a crazy long pass from Joe Carlisle gace Florian Nicot an intercept try to give Montpellier an unassailable lead.
Having reached the semi-finals of Europe's second-tier competition last season and finished as runners-up the year before that, Mike Ruddock's men had openly talked of their desire to go one step further this time around.
But they now face an uphill struggle after a Montpellier side missing star players Francois Trinh-Duc and Fulgence Ouedraogo and lying 13th in the Top 14 inflicted the Warriors' first home defeat of the season.
Carlisle had been on the pitch for less than two minutes when he made the critical mistake as Worcester attempted to move the ball wide.
Nicot gratefully accepted the gift and raced home unopposed and a successful conversion enabled Montpellier to open up a 22-10 lead with little more than half an hour remaining.
Worcester did hit back four minutes later with a second try from Powell - and their second from a powerful driving maul - but it was not enough to prevent a disappointing start to their European adventure.
Tries: Sanderson, Powell
Cons: Walker 2
Pens: Todeschini 4, Schutte
Yellow cards: Bowley (Worcester, 20), Macurdy (Montpellier, 37)
Worcester: 15 Chris Latham, 14 Marcel Garvey, 13 Rico Gear, 12 Dale Rasmussen, 11 Miles Benjamin, 10 Willie Walker, 9 Jonny Arr, 8 Netani Talei, 7 Pat Sanderson, 6 Tom Wood, 5 Graham Kitchener, 4 Will Bowley, 3 Shaun Ruwers, 2 Aleki Lutui, 1 Matt Mullan.
Replacements: 16 Adam Black, 17 Jordan Page, 18 Tevita Taumoepeau, 19 Craig Gillies, 20 Matt Cox, 21 Ryan Powell, 22 Joe Carlisle, 23 Greg King.
Montpellier: 15 Jaques Schutte, 14 Manoel Dall'inga, 13 Ollie Smith, 12 Florian Nicot, 11 Adrien Pratmarty, 10 FÃ©dÃ©rico Todeschini, 9 Adrien Tomas, 8 Marc Giraud, 7 JÃ©rome VallÃ©e, 6 Vassili Bost, 5 Michel Macurdy, 4 Mickael Demarco, 3 Bruce Douglas, 2 Mickael Ladhuie, 1 EugÃ¨ne Van Staden.
Replacements: 16 Joan Caudullo, 17 Na'ama Leleimalefaga, 18 Drickus Hancke, 19 Maxime Castell, 20 Mathieu Petitdemange, 21 Sebastien Max, 22 Jean Matthieu Alcalde, 23 Kevin Kervarec.
Referee: Carlo Damasco (Italy)