Five penalties from Nick Evans proved enough for Harlequins to take a 15-9 Amlin Challenge Cup win over Connacht on Friday.
Evans kicked all his side's points in the first half to give Harlequins the double over Connacht in Pool One and kept them on course for a quarter-final slot.
After their 20-9 victory over the Irishmen at The Stoop the previous weekend, Harlequins knew a win in Galway would effectively rule out last season's semi-finalists from qualification and keep them apace with table-topping Bayonne.
And, with the French Top 14 outfit due to come to London in round six, this was the pivotal match for the visitors.
The extreme weather made conditions difficult, but the hundreds of tons of straw that had been laid on the Sportsground turf made the pitch perfectly playable.
The first half saw Connacht defend well and make life difficult for Quins moving forward, meaning Evans had to dictate the course of events largely with his boot.
The former New Zealand international's goalkicking was also very much in evidence as he landed five out of six shots in an error-strewn and penalty-laden opening 40 minutes.
Welsh referee James Jones' whistle allowed the kickers on both teams to tee up nine shots at goal before the break.
Miah Nikora's two penalties twice got Connacht back on level terms and Ian Keatley added another just before half-time to keep the hosts in touch, but there was no further score after the interval.
The second half started in a near blizzard and with the home side increasing their intensity.
Quins were a man down, with centre Jason Turner-Hall in the sin-bin for an off-the-ball offence spotted by the touch judge, but it was not long before Connacht were reduced to 14 men as well.
Replacement lock Bernie Upton was caught using his elbow illegally as he drove into a ruck on the visitors' 22 and referee Jones sent him to the sidelines for 10 minutes.
Quins lost Tom Guest, Ceri Jones and Gonzalo Camacho to injuries in the first 50 minutes and failed to take advantage of their extra man on two occasions. Prop Jamie Hagan became the second home forward to end up in the bin 10 minutes from time when he went off his feet at a ruck.
That allowed Quins to launch a last-gasp attack. They got up to the line but not over it as wave after wave of forward drives were held inches short, but they had already done enough.
Pens: Nikora 2, Keatley
Pens: Evans 5
Yellow cards: Hagan, Upton (Ulster); Turner-Hall (Harlequins)
Connacht: 15 Gavin Duffy, 14 Darragh Fanning, 13 Ian Keatley, 12 Keith Mathews, 11 Fionn Carr, 10 Miah Nikora, 9 Frank Murphy, 8 John Muldoon, 7 Jonny O'Connor, 6 Andrew Browne, 5 Mike McCarthy, 4 Michael Swift, 3 Jamie Hagan, 2 Sean Cronin, 1 Ronan Loughney.
Replacements: 16 Adrian Flavin, 17 Robert Sweeney, 18 Barry Fa'amausili, 19 Bernie Upton, 20 Mike McComish, 21 Cillian Willis, 22 Troy Nathan, 23 Brian Tuohy.
Harlequins: 15 Mike Brown, 14 Gonzalo Camacho, 13 George Lowe, 12 Jordan Turner-Hall, 11 Tom Williams, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw, 6 Tom Guest, 5 Peter Browne, 4 Ollie Kohn, 3 James Johnston, 2 Joe Gray, 1 Ceri Jones.
Replacements: 16 Matt Cairns, 17 Joe Marler, 18 Mark Lambert, 19 Tomas Vallejos, 20 Will Skinner, 21 Karl Dickson, 22 Rory Clegg, 23 Tom Casson.
Venue: The Sportsground
Referee: James Jones (Wales)
Assistant referees: Phil Fear (Wales), Wayne Davies (Wales)