Northampton strengthened their position at the top of Pool One thanks to a 23-15 victory against Cardiff Blues at Franklin's Gardens on Saturday.
Five yellow cards were shown in a tetchy affair but Saints just about had the better of their visitors with scores from Paul Diggin and Chris Ashton adding to a good kicking effort from Stephen Myler. All of Cardiff's points came via the boot of Dan Parks, who missed just one long-ranger.
Defeat for the Blues means that they now must win the return fixture against Saints in Cardiff next week to keep their last-eight hopes alive.
Cardiff Blues Director of Rugby Dai Young had complained about the legality of the home scrum in the build-up to the game and the Blues were the first to benefit as French referee Roman Poite paid close attention to the set piece.
After Parks landed a third-minute penalty to kick the away side into the lead, the Saints scrum was penalised in the sixth and eighth minute.
But the home pack quickly sorted out their problems to exert intense pressure on the Cardiff scrum which fell foul of the referee four times as they defended desperately.
Soane Tonga'uiha's barnstorming run down the right wing set up the offensive. Cardiff did well to keep the giant Tongan and flanker Tom Wood out before running into scrum trouble.
They conceded two penalties and a free-kick to the right of the posts before Northampton, opting for scrums rather than kicking for goal, moved the ball through several pairs of hands where the Cardiff scrum came up and was penalised again.
Following yet another scrum, Northampton scrum-half Ryan Powell whipped the ball out to Diggin who squeezed over in the corner, with Myler landing the conversion from wide out.
But, despite being on the receiving end for most of the first half, Cardiff led at the interval thanks to the consistent long-range kicking of Parks.
He struck from 40 metres on the half hour after Hartley illegally ripped the ball out of a ruck and again from a similar distance four minutes later for another hands-in-the-ruck offence to put his side 9-7 ahead.
Two minutes later, he landed again from just inside the Northampton half after Saints centre James Downey was yellow-carded for a high tackle on Cardiff's Wales winger Tom James.
But Cardiff's numerical advantage lasted only two minutes before prop Tau Filise followed Downey to the sin bin for handling the ball in the ruck, a decision which had Blues skipper complaining forcibly to the referee at half-time.
Myler reduced the Northampton deficit to two points with the resulting penalty and the Saints took the lead two minutes into the second half after coming out with all guns firing.
Roger Wilson was hauled down just short of the Cardiff line and then the visitors used all their defensive strength to stop the Northampton pack rumbling over their line.
But the numbers required left them short of resources out wide and the Saints whipped the ball to England full-back Ben Foden who sent Ashton over, with Myler again converting to restore the Northampton lead.
Two more Myler penalties, in the 54th and 66th minutes, ensured that Cardiff did not even have the consolation of a losing bonus point to show for their efforts despite a further penalty from Parks after England lock Courtney Lawes was sin-binned for playing the ball when he was off his feet.
Despite being a man down, Northampton should have had another try when James completely missed Myler's high kick to the corner - but Ashton spilled the chance before booting the ball into the crowd in self-disgust.
There was still time for hookers Dylan Hartley, of Northampton, and Gareth Williams, of the Blues, to be yellow-carded in the 76th minute for their part in a pack punch-up and, to add to the drama, there was a brief hold-up when some of the floodlights failed.
Tries: Diggin, Ashton
Con: Myler 2
Pen: Myler 3
For Cardiff Blues:
Pen: Parks 5
Northampton: 15 Ben Foden, 14 Chris Ashton, 13 Jon Clarke, 12 James Downey, 11 Paul Diggin, 10 Stephen Myler, 9 Ryan Powell, 8 Roger Wilson, 7 Tom Wood, 6 Phil Dowson, 5 Christian Day, 4 Courtney Lawes, 3 Brian Mujati, 2 Dylan Hartley (capt), 1 Soane Tonga'uiha.
Replacements: 16 Brett Sharman, 17 Regardt Dreyer, 18 Tom Mercey, 19 Mark Sorenson, 20 Calum Clark, 21 Lee Dickson, 22 Shane Geraghty, 23 Joe Ansbro.
Cardiff Blues: 15 Chris Czekaj, 14 Richard Mustoe, 13 Casey Laulala, 12 Tom Shanklin, 11 Tom James, 10 Dan Parks, 9 Richie Rees, 8 Xavier Rush, 7 Martyn Williams, 6 Maama Molitika, 5 Paul Tito (capt), 4 Bradley Davies, 3 Taufa'ao Filise, 2 Gareth Williams, 1 Gethin Jenkins.
Replacements: 16 Rhys Williams, 17 Scott Andrews, 18 John Yapp, 19 Michael Paterson, 20 Sam Warburton, 21 Tom Slater, 22 Ceri Sweeney, 23 Gavin Evans.
Referee: Romain Poite (France)
Assistant referees: Christophe Berdos (France), Cyril Lafon (France)