Toulouse took control of Heineken Cup Pool 3 with a 17-16 victory over Saracens in an enthralling battle at Wembley Stadium on Friday.
The result is Sarries' first defeat of the season in any competition after being outscored two tries to one in a gripping tussle that went right down to the wire.
Saracens led 13-7 at half time thanks to a try created and scored by centre Chris Wyles but Toulouse were still very much still in the game at the interval after the power of their pack saw them pull a try back with an unstoppable rolling maul.
By their standards, Toulouse were poor in the first half, putting on a disjointed performance that saw them cough up possession far too often as they tried to play expansive rugby in all the wrong areas.
Sarries were more than happy to cash-in on the French side's mistakes and were good value for their six-point lead at the break, though it could have been a very different story had Luke McAlister not let nine points go abegging from the kicking tee.
The second half started in similar fashion but the impact of the Toulouse bench proved critical as the likes of Louis Picamoles, Jano Vermaak and Gurthro Steenkamp turned the tide.
Indeed, it would be Picamoles who used his sheer power to score what proved to be the winning try.
Saracens were first to score, punishing McAlister for a bad decision and worse pass to Clement Poitrenaud, who fumbled. From the turnover ball, Wyles stepped past Gillian Galan to burst clear, finding Ashton up in support before getting it back and cruising over. The TMO gave his rubber stamp despite suspicions of a forward pass from Ashton.
McAlister missed from long range before fluffing a sitter but his pack made amends with an incredible maul from a long way out to put Christopher Tolofua over. Jean-Marc Doussain took over the kicking duties and, like Owen Farrell ten minutes earlier, slotted the conversion to level the scores at 7-all.
Farrell landed two more penalties as things went downhill for Toulouse, who saw McAlister leave the field with a hand injury.
Farrell extended the lead after the break as the Saracens scrum earned a telling scrum penalty and at 16-7, Toulouse had it all to do if they wanted to head home with points.
But les Toulousains would dominate the next 20 minutes, picking and driving in impressive fashion. Saracens did brilliantly to withstand the barrage however, only conceding a single penalty from Doussain to leave the scores at 16-10 going into the final fifteen minutes.
However the momentum was all with Toulouse, who were now making the right decisions in the right areas. Yoann Huget, found space out wide, kicked ahead and followed up to force Alex Goode over his line for a five metre scrum. Bulldozing Picamoles picked up from the back of the scrum and just managed to roll the ball on to the line.
The conversion was booted by Doussain to put Toulouse ahead for the first time with ten minutes left.
Saracens had two late attempts to win through the boot of Farrell, but his long-range penalty came up short before missing with a drop.
Pens: Farrell 3
Yellow card: Strettle
Tries: Tolofua, Picamoles
Cons: Doussain 2
Saracens: 15 Alex Goode, 14 Chris Ashton, 13 Chris Wyles, 12 Duncan Taylor, 11 David Strettle, 10 Owen Farrell, 9 Richard Wigglesworth, 8 Ernst Joubert, 7 Will Fraser, 6 Billy Vunipola, 5 Alistair Hargreaves, 4 Steve Borthwick (c), 3 Matt Stevens, 2 Schalk Brits, 1 Mako Vunipola.
Replacements: 16 Jamie George, 17 Rhys Gill, 18 James Johnston, 19 George Kruis, 20 Kelly Brown, 21 Neil de Kock, 22 Marcelo Bosch, 23 Joel Tomkins.
Toulouse: 15 Maxime Medard, 14 Yoann Huget, 13 Florian Fritz (c), 12 Clement Poitrenaud, 11 Hosea Gear, 10 Luke McAlister, 9 Jean-Marc Doussain, 8 Gillian Galan, 7 Thierry Dusautoir, 6 Yannick Nyanga (c), 5 Joe Tekori, 4 Yoann Maestri, 3 Census Johnston, 2 Christopher Tolofua, 1 Schalk Ferreira.
Replacements: 16 Chiliboy Ralepelle, 17 Gurthro Steenkamp, 18 Yohan Montes, 19 Gregory Lamboley, 20 Romain Millo-Chluski, 21 Jano Vermaak, 22 Gael Fickou, 23 Louis Picamoles.
Venue: Wembley Stadium
Referee: Nigel Owens (Wales)
Assistant referees: Sean Brickell (Wales), Wayne Davies (Wales)
Television match official: Derek Bevan (Wales)