Harlequins kept their qualification hopes alive after sealing a 17-3 win over Racing MÃ©tro, making it back-to-back triumphs over the Parisians.
The win leaves them four points off Pool 4 leaders Clermont with two rounds to play. Les Jaunards will come to the Stoop in Round 5 next month.
Racing meanwhile remain at the bottom as their star-studded line-up continue their dire form in Europe, despite a slight improvement on Sunday.
Quins though got the job done in a professional manner as a try at the end of the first-half from Charlie Walker sent them in 14-0 ahead.
The second-half would be a drab affair, however, as only the boots of Nick Evans, Ben Botica and Jonathan Sexton troubled the scorers.
Having demolished Racing the previous week, the hosts were looking to repeat the bonus-point triumph of round three to keep them in contention of qualifying for the quarter-finals.
Despite losing their first two encounters in this year's Heineken Cup, that thrashing of the Top 14 outfit had kept their hopes alive.
However, with Quins looking to play an up tempo game, the weather hampered their chances of keeping the ball in the hands.
But with Danny Care and Evans directing operations at half-back and Chris Robshaw and Nick Easter carrying with vigour, the hosts always looked dangerous.
The opening period was played almost exclusively in Racing's half and it was no surprise to see them take the lead from the boot of their fly-half.
Evans added his second from the tee soon after before another three-pointer - following a yellow card to Davit Khinchagishvili - gave them a 9-0 advantage after 25 minutes.
Although the visitors had a brief visit into the opposition 22, Luke Wallace was a constant thorn, turning the ball over on a number of occasions.
And the pressure eventually told on the away side's rearguard when Walker crossed the whitewash to take Harlequins 14-0 ahead at the break.
Conor O'Shea's men continued their stranglehold on proceedings in the second period and Botica - on for the injured Evans - kicked a penalty.
Sexton did finally get Metro on the board when they bizarrely opted to go for the posts when 17 points down.
Racing did press for a try late on but the hosts comfortably held on.
Pen: Evans 3, Botica
For Racing Metro:
Harlequins: 15 Mike Brown, 14 Charlie Walker, 13 Matt Hopper, 12 Tim Molenaar, 11 Sam Smith, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw (c), 6 Luke Wallace, 5 George Robson, 4 Charlie Matthews, 3 Will Collier, 2 Dave Ward, 1 Joe Marler.
Replacements: 16 Kyle Sinckler, 17 Mark Lambert, 18 Paul Doran Jones, 19 Nick Kennedy, 20 Joe Trayfoot, 21 Karl Dickson, 22 Ben Botica, 23 Ollie Lindsay-Hague.
Racing Metro: 15 Juan MartÃn HernÃ¡ndez, 14 Adrien PlantÃ©, 13 Henry Chavancy, 12 Jamie Roberts, 11 Virimi Vakatawa; 10 Jonny Sexton, 9 Mike Phillips, 8 Camille Gerondeau, 7 Antoine Battut (c), 6 Dan Lydiate, 5 Karim Ghezal, 4 Fabrice Metz, 3 Soane Tonga'uiha, 2 Virgile Lacombe, 1 Davit Khinchagishvili.
Replacements: 16 Jeremie Maurouard, 17 Eddy Ben Arous, 18 Luc Ducalcon, 19 Juandre Kruger, 20 Bernard Le Roux, 21 Maxime Machenaud, 22 Jonathan Wisniewski 23 Benjamin Fall.
Referee: Alain Rolland (Ireland)
Assistant referees: Sean Gallacher, Gary Conway (both Ireland)
TMO: Simon McDowell (Ireland)