Danny Care scored a brace of tries as Harlequins downed Connacht 22-30 in their Heineken Cup Pool 3 at the Galway Sportsground.
The reigning English Champions had to dig deep to make it back-to-back success stories following their bonus-point triumph against Biarritz Olympique Pays Basque.
A brace of tries from England scrum-half Danny Care turned the game in Quins' favour just before the break as the visitors scored 15 unanswered points in the final 10 minutes of the half.
Care crossed on the half-hour mark and then again seven minutes later, with Ben Botica converting once and adding another penalty in injury time at the end of the first period.
Connacht ran out narrow winners in this fixture last season and the Irish province looked to be heading towards another famous upset when a sixth-minute Dave McSharry try was complimented by a fine kicking display from Dan Parks that saw the hosts lead 10-6 and then 19-9 after 27 minutes.
But Care's quick-fire brace handed Harlequins a 24-19 advantage at the break, with neither side able to add to their try-scoring tally in a nerve-wracking second half.
Parks closed the gap to just two points with a fifth penalty four minutes after the restart but it was as close as Connacht came to repeating their Round 1 win at Zebre.
Botica continued his assured form at fly-half to kick two more penalties after being asked to stand in for the injured Nick Evans as he finished with a personal tally of 20 points seven days after bagging 18 when replacing his fellow Kiwi against Biarritz.
Final Score Connacht 22 (19) Harlequins 30 (24)
Penalties: Parks 5
Tries: Care 2
Penalties: Botica 6
Referee: Jerome Garces (Fra),
Assistant ref: Sebastian Cloute,
Assistant ref: Salam Attalah,
TMO: Eric Gauzins,
Citing Commissioner: Iain Goodall
Connacht Rugby: Robbie Henshaw; Tiernan O'Halloran, Eoin Griffin, David McSharry, Fetu'u Vainikolo; Dan Parks, Kieran Marmion; Dennis Buckley, Adrian Flavin, Nathan White (c), Michael Swift, Mike McCarthy, John Muldoon, Willie Faloon, George Naoupu.
Replacements: Jason Harris-Wright, Brett Wilkinson, Ronan Loughney, David Gannon, Jonny O'Connor, Dave Moore, Miah Nikora, Mata Fifita.
Harlequins: Mike Brown; Tom Williams, Matt Hopper, Jordan Turner-Hall, Sam Smith; Ben Botica, Daniel Care; Joe Marler, Rob Buchanan, James Johnston, Ollie Kohn, George Robson, Maurie Fa'asavalu, Chris Robshaw (c), Nick Easter.
Replacements: David Ward, Mark Lambert, Will Collier, Charlie Matthews, Tom Guest, Karl Dickson, Rory Clegg, Seb Stegmann.