Jack Nowell scored a hat-trick as Exeter Chiefs ran riot at the Stoop to book a home semi-final in Aviva Premiership Rugby against Wasps.
James Short, Nowell and Dave Ewers crossed in the first half before Danny Care responded just before half-time.
But Exeter, who will host a Wasps side in the semi-finals they beat 24-3 just a week ago, raced out of the blocks after the break with a second Short try sandwiched between two Nowell scores.
Further tries came through Will Chudley, Julian Salvi, Phil Dollman and a sublime Henry Slade, the outside centre an outlet all afternoon, while Kyle Sinckler and Winston Stanley grabbed Harlequins consolations.
Ultimately it was a frustrating result for Conor O’Shea in his last home game in charge for Harlequins, who end the season seventh but can still qualify for the Champions Cup should they beat Montpellier in the Challenge Cup final.
Nick Evans opened proceedings with a fourth-minute penalty before Short started the Chiefs assault six minutes later.
Taking advantage of the space afforded to him on the left wing, Short burst over the line and two minutes later, Nowell added a second try out on the right following a series of pick-and-goes from close quarters.
Steenson kicked just one conversion from three but Chiefs were nonetheless storming to a home semi-final, as Nowell harried Ross Chisholm out of play following a brilliant Slade kick to set up the third try in the 20th minute.
From the lineout, Chiefs needed just two phases before flanker Ewers barged over, and Steenson found his kicking boots to complete the conversion and stretch the lead out to 17-3.
Harlequins would have hit back almost immediately if not for superb Chiefs defending on the line led by Nowell, just as his England teammate Care looked to have squirmed through. Replays proved inconclusive and no try was awarded.
In the final minute of the half Care got his rewards however, Mike Brown and Marland Yarde linking up before setting the Harlequins skipper away – Evans adding the conversion.
Exeter wrapped up the bonus point three minutes into the second half when a long pass thrown over the head of Chisholm fell to Nowell who ran over untroubled.
Short followed suit shortly after with his second as he evaded the tackle on the left touchline to cross over before Steenson made it 29-10 with a fine touchline kick.
Nowell crossed for his third try on 53 minutes in what was to be his last action of the match.
Harlequins responded through sub prop Sinckler but Dollman then sliced through a wilting defence and the half-ton came up when Chudley went in under the posts.
Slade was soon set away for his score on the right and while Stanley’s try reduced the gap momentarily, the Chiefs scored an incredible tenth effort in the corner seconds later through Salvi.