Harlequins cemented their position at the top of Pool 3 after recording a 30-22 victory over Connacht on Saturday.
In an entertaining opening half, it was the visitors who led 24-19 at the break after a double from England international Danny Care with the rest of their points coming from the boot of Ben Botica.
The Irish province had taken a 19-9 advantage through Dave McSharry's converted try and four Dan Parks' penalties. Despite the second half being a slightly more disappointing affair, the visiting stand-off added two further three-pointers to Parks' one to seal the win.
Connacht famously ousted Quins from the competition last season after defeating the English team 9-8 in windy conditions. They hinted at a similar outcome in the early exchanges.
Although Botica continued his fine kicking form from last week with a third minute penalty, McSharry touched down for the hosts.
The respective fly-halves then traded penalties as the Irish province opened up a 10-6 advantage after 12 minutes. Botica reduced the arrears from the tee before three successive three-pointers by Parks extended the home side's advantage.
It was at that moment when the visitors lifted the tempo and the Galway-based outfit struggled to cope. Care got the first of his tries after finding a gap in the opposition's defence following a scrum on the 22.
He then sniped around the fringes once again to put Harlequins level. The visitors' fly-half converted to give them the lead before the same player added a late penalty as Quins opened up a five-point cushion at the interval.
Parks and Botica traded penalties early in the second period as the score moved to 27-22 in the English team's favour. And Botica confirmed the win with a final three-pointer.
Pens: Parks 5
Try: Care 2
Pens: Botica 6
Connacht: 15 Robbie Henshaw, 14 Tiernan O'Halloran, 13 Eoin Griffin, 12 Dave McSharry, 11 Fetu'u Vainikolo, 10 Dan Parks, 9 Kieran Marmion, 8 George Naoupu, 7 Willie Faloon, 6 John Muldoon, 5 Mike McCarthy, 4 Michael Swift, 3 Nathan White, 2 Adrian Flavin, 1 Dennis Buckley.
Replacements: 16 Jason Harris Wright, 17 Brett Wilkinson, 18 Ronan Loughney, 19 Dave Gannon, 20 Johnny O'Connor, 21 Dave Moore, 22 Miah Nikora, 23 Mata Fifita.
Harlequins: 15 Mike Brown, 14 Tom Williams, 13 Matt Hopper, 12 Jordan Turner-Hall, 11 Sam Smith, 10 Ben Botica, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw, 6 Maurie Fa'asavalu, 5 George Robson, 4 Ollie Kohn, 3 James Johnston, 2 Rob Buchanan, 1 Joe Marler.
Replacements: 16 Dave Ward, 17 Mark Lambert, 18 Will Collier, 19 Charlie Matthews, 20 Tom Guest, 21 Karl Dickson, 22 Rory Clegg, 23 Seb Stegmann.