Four-time champions Toulouse cruised past two-time winners Leicester 23-9 in the torrential rain on Sunday in a battle of European Cup heavyweights.
The win could prove crucial in a Pool Two which also includes powerful Welsh side Ospreys who had opened their campaign with a bonus point 38-17 win over Treviso on Friday.
Toby Flood had kicked Leicester 9-6 ahead by the 35th minute with three penalties to a brace from former All Black Luke McAlister to briefly give the English side hope of repeating Harlequins' shock win at Toulouse last season.
But the game turned on a fine individual try by highly-rated centre Gael Fickou just before the interval.
Leicester's Thomas Waldrom lost the ball at the halfway line, 18-year-old Fickou kicked ahead, outsprinting his pursuers to score what was the only try of the game much to the delight of the 38,000 crowd.
McAlister missed the conversion but went on to kick four second-half penalties as Toulouse flexed their muscles.
"With the rain falling heavily, it was a really difficult match," said Toulouse coach Guy Noves.
"It was tough so I can only congratulate my players for rolling up their sleeves although it was unfortunate that we didn't score one or two more tries and kill off the opposition."
Leicester coach Richard Cockerill admitted his side had paid the price for not hammering home their advantage when they were ahead.
"We controlled the match for 38 minutes when we kept up a three-point lead and we wanted to take the match in hand," he said.
"But we weren't able to do it for more than the first half and we have to be better than that. We didn't do it and we were punished for it."
Earlier on Sunday, Northampton clawed back 15 unanswered points to defeat Glasgow 24-15 in Pool Four and Sale trumped Cardiff Blues in a 34-33 Pool Six thriller.
Glasgow roared into a 15-point lead thanks to tries by Josh Strauss and Sean Lamont, Peter Horne nailing a penalty and conversion.
But Saints' stand-out Samoan centre George Pisi hit back with two tries, one converted by Stephen Myler, to make it 15-12 to the visitors at the break.
Myler then crossed for a try minutes after the break and Russian wing Vasily Artemyev also touched down to ensure a bonus-point victory for Northampton, European champions back in 2000.
"We were under a bit of pressure, but what was pleasing was the way we came back and kept our composure. In the second half, we controlled the game," said Saints coach Jim Mallinder.
"I think we are in decent shape. When we are on top of our game we are a hard side to beat, and we need to keep at that intensity every single week."
In Salford, Sale left it late in beating Cardiff Blues, for whom Wales wing Alex Cuthbert scored a hat-trick, all converted by fullback Leigh Halfpenny who also notched up four penalties.
However, that haul was not enough as Sale, whose league form has so far this season been woeful, launched a comeback inspired by a Danny Cipriani try with 25 minutes remaining.
Mark Jennings and Tony Buckley also crossed the whitewash and, allied with 12 points from Nicky MacLeod's boot and Rob Miller providing a crucial penalty and two conversions at the death, Sale grabbed an unlikely yet vital victory.
"It's something we've been longing for," said Cipriani, whose Sale team went into the game having lost five matches in succession.
"We had to give the fans something to cheer about and we did."
In Sunday's late Pool Six game, Toulon ran in five tries for a bonus-point 37-16 win over fellow French side Montpellier with English fullback Delon Armitage scoring twice.
Pierrick Gunther, Mathieu Bastereaud and South African lock Bakkies Botha also crossed for tries.
All the teams and scorers:
Toulouse 23-9 Leicester
Pens: McAlister 6
For Leicester Tigers:
Pens: Flood 3
Toulouse: 15 Clement Poitrenaud, 14 Vincent Clerc, 13 Florian Fritz, 12 Gael Fickou, 11 Yoann Huget, 10 Luke McAlister, 9 Jean Marc Doussain, 8 Louis Picamoles, 7 Thierry Dusautoir (captain), 6 Yannick Nyanga, 5 Yoann Maestri, 4 Romain Millo Chlusky, 3 Census Johnston, 2 Gary Botha, 1 Gurthro Steenkamp.
Replacements: 16 Christopher Tolofua, 17 Jean Batiste Poux, 18 Antoine Guillamon, 19 Patricio Albacete, 20 Jean Bouilhou, 21 Yannick Jauzion, 22 Luke Burgess, 23 Timoci Matanavou.
Leicester Tigers: 15 Scott Hamilton, 14 Niall Morris, 13 Manu Tuilagi, 12 Anthony Allen, 11 Vereniki Goneva, 10 Toby Flood, 9 Ben Youngs, 8 Jordan Crane (captain), 7 Thomas Waldrom, 6 Steve Mafi, 5 Geoff Parling, 4 Graham Kitchener, 3 Dan Cole, 2 Tom Youngs, 1 Logovi'i Mulipola.
Replacements: 16 George Chuter, 17 Marcos Ayerza, 18 Martin Castrogiovanni, 19 Ed Slater, 20 Richard Thorpe, 21 Sam Harrison, 22 George Ford, 23 Matt Smith.
Northampton Saints 24-15 Glasgow Warriors
For Northampton Saints:
Tries: G Pisi 2, Myler, Artemyev
Cons: Myler, Lamb
For Glasgow Warriors:
Tries: Strauss, Lamont
Northampton Saints: 15 James Wilson, 14 Ken Pisi, 13 George Pisi, 12 Dom Waldouck, 11 Vasily Artemyev, 10 Stephen Myler, 9 Lee Dickson, 8 Rhys Oakley, 7 Tom Wood, 6 Phil Dowson, 5 Courtney Lawes, 4 Samu Manoa, 3 Brian Mujati, 2 Dylan Hartley (captain), 1 Soane Tonga'uiha.
Replacements: 16 Mike Haywood, 17 Alex Waller, 18 Paul Doran Jones, 19 Mark Sorenson, 20 GJ Van Velze, 21 Martin Roberts, 22 Ryan Lamb, 23 Tom May.
Glasgow Warriors: 15 Stuart Hogg, 14 Tommy Seymour, 13 Alex Dunbar, 12 Peter Horne, 11 Sean Lamont, 10 Ruaridh Jackson, 9 Henry Pyrgos, 8 Ryan Wilson, 7 John Barclay, 6 Josh Strauss, 5 Al Kellock (captain), 4 Tim Swinson, 3 Mike Cusack, 2 Dougie Hall, 1 Ryan Grant.
Replacements: 16 Finlay Gillies, 17 Ofa Fainga'anuku, 18 Gordon Reid, 19 Tom Ryder, 20 Chris Fusaro, 21 James Eddie, 22 Niko Matawalu, 23 Peter Murchie.
Sale Sharks 34-33 Cardiff Blues
Tries: Cipriani, Jennings, Buckley
Cons: Miller 2
Pens: MacLeod 4 Miller
Tries: Cuthbert 3
Cons: Halfpenny 3
Pens: Halfpenny 4
Sale Sharks: 15 Rob Miller, 14 Mark Jennings, 13 Will Addison, 12 Sam Tuitupou, 11 Mark Cueto, 10 Nick Macleod, 9 Nathan Fowles, 8 Andy Powell, 7 David Seymour (captain), 6 Richie Vernon, 5 Fraser McKenzie, 4 Richie Gray, 3 Tony Buckley, 2 Tommy Taylor, 1 Eifion Lewis-Roberts.
Replacements: 16 Joe Ward, 17 Ross Harrison, 18 Vadim Cobilas, 19 Kearnan Myall, 20 James Gaskell, 21 Cillian Willis, 22 Danny Cipriani, 23 Johnny Leota.
Cardiff Blues: 15 Leigh Halfpenny, 14 Alex Cuthbert, 13 Gavin Evans, 12 Jamie Roberts, 11 Tom James, 10 Ceri Sweeney, 9 Lloyd Williams, 8 Andries Pretorius (captain), 7 Sam Warburton, 6 Josh Navidi, 5 Lou Reed, 4 Bradley Davies, 3 Benoit Bourrust, 2 Marc Breeze, 1 Tafa'ao Filise.
Replacements: 16 Andi Kyriacou, 17 Nathan Trevett, 18 Scott Andrews, 19 James Down, 20 Robin Copeland, 21 Lewis Jones, 22 Gareth Davies, 23 Dan Fish.
Toulon 37-16 Montpellier
Tries: D Armitage, Botha, Gunther, Bastareaud
Cons: Wilkinson 2, Giteau
Pens: Wilkinson 2
Pens: Perraux 2, Paillaugue
Toulon: 15 Delon Armitage, 14 Vincent Martin, 13 Maxime Mermoz, 12 Matt Giteau, 11 David Smith, 10 Jonny Wilkinson (captain), 9 Frederic Michalak, 8 Chris Masoe, 7 Steffon Armitage, 6 Pierrick Gunther, 5 Jocelino Suta, 4 Bakkies Botha, 3 Carl Hayman, 2 Sebastien Bruno, 1 Andrew Sheridan.
Replacements: 16 Mickael Ivaldi, 17 Gethin Jenkins, 18 Virgile Bruni, 19 Mathieu Bastareaud, 20 Benjamin Lapeyre, 21 Sébastien Tillous-Borde, 22 Simon Shaw, 23 Davit Kubriashvili.
Montpellier: 15 Lucas Amorosino, 14 Yoan Audrin, 13 Matt Carraro, 12 Paul Bosch, 11 Yohann Artru, 10 Ilian Perraux 9 Julien Tomas (captain), 8 Johnnie Beattie, 7 Rémy Martin, 6 Alexandre Bias, 5 Mickael Demarco, 4 Drickus Hancke, 3 Maximiliano Bustos, 2 Mickael Ladhuie, 1 Yvan Watremez.
Replacements: 16 Agustin Creevy, 18 George Jgenti, 19 Aliki Fakate, 20 Mamuka Gorgodze, 21 Benoit Paillaugue, 22 Pierre Bérard, 23 Timoci Nagusa.