Harlequins' fourteen-game winning streak came to a grinding halt on Friday as they succumbed 21-10 at home to Toulouse in the Heineken Cup.
The four-time European champions led from start to finish, outscoring their hosts two tries to one in an impressive display to take control of Pool Six.
Fijian wing Timoci Matanavou touched down on either side of half time for the visitors while full-back Mike Brown scored for Quins' early in the second period.
Toulouse led 11-3 at the break and while Brown's score briefly narrowed the gap to a single point, the French visitors never realistically looked like losing.
Indeed, les Toulousains were consistently a step ahead of Quins, who didn't seem to have an answer to the French club's outstanding defence and efficiency at the breakdown.
Harlequins got an insight into the size of the task ahead of them in the first minute when their young winger Sam Smith was driven and unceremoniously dumped into touch by his opposite number Matanavou.
After Luke McAlister and Nick Evans exchanged penalties, Matanavou then showed his attacking prowess by touching down in the corner.
He applied the finish after French international forwards Louis Picamoles and Thierry Dusautoir had expertly created the space for him.
Toulouse dominated the remainder of the first half and Quins struggled to deal with their power and expertise at the breakdown but the French club only managed to add three more points and the game was still finely poised at 11-3 at the break.
The home team came out re-energised and fired up for the second period and after some good possession, they made the breakthrough.
After a great initial break from deep inside his own half by centre Matt Hopper, the Premiership leaders were awarded a kickable penalty.
Danny Care opted for the quick tap though and it paid off after Brown picked a great line and crashed over to make it 11-10 following the successful conversion.
McAlister took the heat out of Harlequins' resurgence with three points soon afterwards and the French Top 14 leaders began to establish their strength, experience and quality once more Quins fought valiantly but the comeback always looked beyond them after the 66th minute, when Matanavou crossed for his second try of the night following a superb, scything break from Vincent Clerc.
The home side never gave up and did have a few chances to claim a losing bonus point but a win over the 2010 champions proved a step too far for them as Toulouse demonstrated their credentials and laid down a marker for every other side in this year's competition.
Tries: Matanavou 2
Pens: McAlister 3
Harlequins: 15 Mike Brown, 14 Seb Stegmann, 13 Matt Hopper, 12 Benjamin Urdapilleta, 11 Sam Smith, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw (c), 6 Maurie Fa'asavalu, 5 George Robson, 4 Tomas Vallejos, 3 James Johnston, 2 Chris Brooker, 1 Joe Marler
Replacements: 16 Joe Gray, 17 Mark Lambert, 18 Kyle Sinckler, 19 Charlie Matthews, 20 Luke Wallace, 21 Richard Bolt, 22 Rory Clegg, 23 Ugo Monye.
Toulouse: 15 Maxime Medard, 14 Vincent Clerc, 13 Florian Fritz, 12 Yannick Jauzion, 11 Timoci Matanavou, 10 Luke McAlister, 9 Luke Burgess, 8 Louis Picamoles, 7 Thierry Dusautoir, 6 Yannick Nyanga, 5 Yoann Maestri, 4 GrÃ©gory Lamboley, 3 Census Johnston, 2 Gary Botha, 1 Jean-Baptiste Poux.
Replacements: 16 William Servat, 17 Yohan Montes, 18 Johnson Falefa, 19 Romain Millo-Chluski, 20 Jean-Marc Doussain, 21 Yves Donguy, 22 Yann David , 23 Shaun Sowerby.
Venue: The Stoop
Referee: George Clancy (Ireland)
Assistant referees: Leo Colgan (Ireland), Ken Beggs (Ireland)
Television match official: Peter Ferguson (Ireland)