Saracens took control of Heineken Cup Pool One thanks to a 37-28 win over Racing Métro, despite being outscored three tries to one in Nantes on Saturday.
Racing led 25-12 after 30 minutes but fell apart in the second half as Sarries fly-half Owen Farrell massacred the hosts from the kicking tee, finishing with a perfect record from eleven attempts at goal.
The result means that victory at home to out-of-form Edinburgh next week will secure Saracens top spot in the pool and a place in the quarter-finals. Racing must travel to Munster in a battle for second place.
The hosts started like a train at Stade de la Beaujoire and, after David Strettle had picked up an early injury, his fellow backs Chris Ashton and Richard Wigglesworth were powerless to stop the enormous prop Luc Ducalcon forcing his way over from short range inside the opening 10 minutes.
Ashton's error under a high ball then afforded Racing the opportunity to run in a second try and Juan Imhoff gleefully accepted it and dived over in the right-hand corner after an excellent floated pass from Fabrice Estebanez.
Imhoff's second and the French side's third then arrived moments later as Juan Martin Hernandez shrugged off Joel Tomkins far too easily before providing the killer pass for his countryman to score in the corner again.
Saracens then lost their discipline as well as their defensive shape as Will Fraser was sent to the sin bin for a late hit on Hernandez and Sebastien Descons added a penalty to his two previous conversions.
Oddly enough, Saracens only faced a 10-point deficit though as Farrell kicked a penalty almost immediately after the kick-off following each of the French team's scores.
Descons slotted over another three points before the half-hour mark but Farrell responded again with two more penalties of his own after Fijian Jone Qovu was sent to the sin bin himself for a late shoulder charge on the Sarries fly-half.
The Londoners will have been delighted to head into the break trailing by just seven points after a whirlwind first half in which they were distinctly second best and they drew level in the early stages of the second half.
They may have been fortunate to have been in touching distance at half-time but their play after the interval owed much more to skill and determination than luck and Chris Wyles got the try to level the scores after great work from Farrell and Tomkins.
Farrell added the conversion and three further penalties to just one from Descons as the second half developed into a far tighter and edgier affair than the first.
Saracens survived another period down to 14 men when Ashton was given a harsh yellow card and they soaked up everything Racing could throw at them before sealing an improbable victory with a remarkable tenth penalty from the flawless boot of their young England fly-half.
For Racing Métro:
Tries: Ducalcon, Imhoff 2
Cons: Descons 2
Pens: Descons 3
Yellow cards: Qovu; Noirot
Pens: Farrell 10
Yellow cards: Fraser, Ashton
Racing Metro: 15 Benjamin Fall, 14 Juan Imhoff, 13 Henry Chavancy, 12 Fabrice Estebanez, 11 Sireli Bobo, 10 Juan Martin Hernandez, 9 Sebastien Descons, 8 Masi Matadigo, 7 Alvaro Galindo, 6 Antoine Battut, 5 Jone Qovu Nailiko, 4 Francois Van Der Merwe, 3 Luc Ducalcon, 2 Dimitri Szarzewski, 1 Eddy Ben Arous.
Replacements: 16 Benkjamin Noirot, 17 Julien Brugnaut, 18 Benjamin Sa, 19 Fabrice Metz, 20 Camille Gerondeau, 21 Jacques Cronje, 22 Mathieu Belie, 23 Olly Barkley.
Saracens: 15 Chris Wyles, 14 Chris Ashton, 13 Joel Tomkins, 12 Brad Barritt, 11 David Strettle, 10 Owen Farrell, 9 Richard Wigglesworth, 8 Ernst Joubert, 7 Will Fraser, 6 Kelly Brown, 5 Mouritz Botha, 4 Steve Borthwick (c), 3 Matt Stevens, 2 Schalk Brits, 1 Rhys Gill.
Replacements: 16 John Smit, 17 Mako Vunipola, 18 Petrus Du Plessis, 19 George Kruis, 20 Nick Fenton-Wells, 21 Neil de Kock, 22 Charlie Hodgson, 23 Duncan Taylor.
Venue: La Beaujoire, Nantes
Referee: Alain Rolland (Ireland)