Paul Gustard’s side produced a fine display and did little wrong, but still turned around 18 points down with first-half Clermont tries coming from Fritz Lee and Damian Penaud, with Camille Lopez kicking two drop-goals.
Mike Brown crossed for Harlequins, but Clermont’s power game proved too much as Morgan Parra also added two conversions and two penalties.
Ultimately it was not enough, but the English side can take real heart from their performance ahead of their final three games of the Gallagher Premiership.
Clermont were straight on the front foot and Lopez opened the scoring as he stepped back into the pocket and struck a sweet drop-goal with his left foot.
Lopez then dropped another goal which was quickly followed by a Parra penalty and although Marler did return to the field, Clermont soon moved further clear.
Number eight Lee crashed on to a pass from Parra and spun out of the tackle to make it to the line. Parra added the conversion for a 16-3 lead.
Harlequins were up against it, but they hit back just before the break when Smith’s superb break and pass on the loop around found full-back Brown, who fended off Penaud to make the line.
Smith could not convert and Parra’s penalty made it 26-8 at the break.
Clermont dominated the early second-half possession and Parra added two more quick penalties as he continued his perfect evening’s work from the tee.
Harlequins wing Ross Chisholm had a try ruled out after Dombrandt was rightly judged by the TMO to have just been in touch, but captain Robshaw soon responded.
The flanker was driven over the line with the help of Matt Symons beneath the posts and Smith could not miss with the conversion.
Smith then kicked ahead and when Clermont full-back Setariki Tuicuvu failed to deal with it, Lang pounced just two minutes after entering the action.
Smith converted and all of a sudden the momentum – against all the odds – was with Harlequins.
Gustard’s side were right up for the challenge and were forcing Clermont into rare mistakes.
Laidlaw then failed to settle the French nerves as he missed with a late penalty and Dombrandt was driven over the line to reduce the gap further still.
Smith’s drop goal conversion hit the post as Harlequins – for whom Semi Kunatani made a remarkable impact off the bench – fell just short against a Clermont side who still have not lost at home this season.
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