|Blues (6) 20|
|Tries: Hobbs Cons: J Evans 2 Pens: Patchell 2|
|Harlequins (3) 32|
|Tries: Visser, Lindsay-Hague, Walker, Care Cons: Botica 2, Swiel Pen: Botica 2|
Harlequins beat Cardiff Blues to earn a second successive European Challenge Cup bonus-point win.
The teams paid tribute to the late All Blacks legend Jonah Lomu with a minute's applause for the former Blues wing before kick-off.
Blues led 6-3 at the break, but tries from Tim Visser, Ollie Lindsay-Hague and Charlie Walker put Quins in charge.
A penalty try and Sam Hobbs' score gave Blues hope, but Matthew Rees' red card and Danny Care's try sealed Quins' win.
Both teams started their campaigns with bonus-point victories but, whereas the Blues made only three changes from their 50-9 win in Calvisano, Harlequins switched eight from their 41-18 triumph against Montpellier.
The hosts seemed to benefit from their continuity in selection, dominating the early exchanges and leading 6-0 thanks to two Rhys Patchell penalties.
A serious-looking head injury to Harlequins captain Jack Clifford prompted a long delay and slowed the game's tempo before the visitors pounded their opponents' try-line.
But they had to settle for a Ben Botica penalty to halve their deficit.
The breakthrough came 10 minutes into the second half, as wing Visser intercepted a loose pass from Kristian Dacey and scampered clear from the halfway line.
The Blues' defence was similarly sloppy 90 seconds later, as full-back Lindsay-Hague skipped past several would-be tacklers to saunter over for a converted try which put his side 20-6 ahead.
Injuries to influential flanker Ellis Jenkins and fly-half Patchell compounded the Blues' problems, before England scrum-half Care came on to deftly create a try for Walker.
Cardiff were given a slither of hope when they were awarded a penalty try with 10 minutes left after a rolling maul was brought down illegally.
A red card for Rees' apparent stamp on Easter's head made their task even tougher, although replacement prop Hobbs did bundle his way over to make it 25-20.
With the final play of the game, Care sped over in the corner to score Harlequins' fourth try, securing a bonus point and denying the Blues theirs.
Cardiff Blues: Blaine Scully, Alex Cuthbert, Rey Lee-Lo, Gavin Evans, Tom James, Rhys Patchell, Lloyd Williams; Gethin Jenkins (capt), Kristian Dacey, Taufa'ao Filise, Jarrad Hoeata, James Down, Josh Turnbull, Ellis Jenkins, Manoa Vosawai,
Replacements: Matthew Rees, Sam Hobbs, Dillon Lewis, Lou Reed, AN Other, Tavis Knoyle, Jarrod Evans, Dan Fish
Harlequins: Ollie Lindsay-Hague; Charlie Walker, Matt Hopper, Harry Sloan, Tim Visser; Ben Botica, Karl Dickson; Mark Lambert, Rob Buchanan, Kyle Sinckler, Charlie Matthews, Sam Twomey, James Chisholm, Jack Clifford (capt), Nick Easter.
Replacements: Joe Gray, Joe Marler, Will Collier, Kieran Treadwell, Dave Ward, Danny Care, Winston Stanley, Tim Swiel.
Referee: Alexander Ruiz (Fra)
Assistant Referees: Laurent Cardona (Fra), Arnaud Blondel (Fra)
TMO: Jean-Marie Piraveau (Fra)
Citing Commissioner: Francesco Grillo (Ita)