Blues coach Dai Young says his side upped their game at the right time to leave Quins losers at the Cardiff City Stadium but rued the cost as his team side suffered a catalogue of injuries.
John Yapp tore a bicep and will be out for four months, Gareth Tomas tore a muscle in his groin and will not play for six weeks, and Bradley Davies' neck injury will keep him off the park for three weeks.
Furthermore, the club are anxiously waiting news on skipper Paul Tito who will undergo a scan after a clash meant he had to withdraw from the field after 38 minutes.
It was a classic European battle, and despite the injuries it could be just what the Blues need to give their season a boost.
Young's side have struggled in the early weeks of the season as injuries have limited his selection, but with Jamie Roberts and Leigh Halfpenny back in the fold, the Blues look a little bit more like the side that almost made it to the Heineken Cup final last term.
And when it was required, the Blues delivered. Home wins in the Heineken Cup are crucial if passage into the final eight is to be secured. And Young knows it.
Young said: "For the first 20 minutes of the second half we changed the tempo f the game and went up a few gears."
"We showed real determination and bottle when we had our backs against the wall to come away with something."
He said: "We are thoroughly pleased with the win, but it turned out to be very expensive."
And Young says his side had to think on their feet in the light of so many enforced replacements. "Our plans went out the window because we had to re-jig so much but in the last 20 minutes, he said.
"But we are still not scoring enough points when we get ahead. To do well in this competition, we should put these games to bed a lot earlier. Instead it was all Harlequins in the last 20 minutes but we showed a lot guts in defence."
The directors of ERC voted unanimously at a Board meeting to postpone all decisions including the release of further instalments of ERC's distributable central revenues to the six shareholder countries until 19 February next when the Board will meet again to reconsider the issue.