Ulster came to the Stoop knowing that qualification for the last 16 of the Champions Cup would be be sealed with a victory of any kind against an in-form Harlequins side, who had ambitions of their own, as they knew a bonus point win would see them move up the table having already qualified.
Quins took the early lead, catching Ulster out with a quick throw at a lineout and the halfway line. Winger, Nick David, collected the ball from Andre Esterhuizen and sprinted clear for an easy try. Marcus Smith added the extra two.
Ulster reacted well, piling on the pressure in Quins 22. A yellow card came fro the try-scorer David, as he intentionally knocked a pass forward in an Ulster attack. Ulster hit back minutes later, with a well worked attacking phase going out wide to find David McCann, who did well to finish in the corner. John Cooney converted the try to level things.
Quins replacement Louis Lynagh had a moment of brillance, as the winger took the ball from a quick tap and charged down the field. Lynagh's kick chase was an awkward one for Jacob Stockdale to deal with, and the powerful winger collected the ball from the bounce and celebrated the home side's second try as he went over. Smith added the extras.
There was a sense of Deja Vu about Quins third try of the half, Lynagh again chased hard after a punt down the field. Robert Baloucoune was back-peddling and an awkward bounce of the ball landed perfectly again for Lynagh to dive over. Ulster had been counter-attacked again and conceded again. It was a sucker punch.
Smith's conversion left the half-time score at 21-7 to the home side.
Ulster's hopes of staging a comeback were dealt a blow when quick-thinking scrum-half Danny Care, took the ball after a lineout in the Ulster 22 and darted through a gap in the Ulster defence.
Smith added another two.
It felt like one of those days for Ulster as a Steven Kitshoff try was ruled out following an earlier knock-on from Harry Sheridan, whose bursting run had created the attack.
Quins weren't finished there, with Care turning provider for centre Andre Esterhuizen who dived over after breaking a tackle. Smith missed on this occasion.
Quins hit their sixth try of the match after Nick David went over for his seocnd of the day following good work from Tyrone Green. Smith wouldn't miss again and made it 40 points to the home side.
Ulster showed fight with Stuart McCloskey bundling over near the posts for a try, however Quins stunted all momentum again with Will Evans intercepting a loose pass and pouncing.
With Ulster pushing for a bonus point try, they were perhaps inches away from doing so.
The away side worked the ball wide and found Rob Baloucoune who spun to plant the ball over the whitewash. However a TMO check confirmed the wing had been pushed into touch.
Ulster would get a third try, with Billy Burn's neat cross-field kick finding Jacob Stockdale, who did well to ground the ball in the corner.
As the whistle blew, Ulster knew their Champions Cup campaign had ended on a sour note and that the team would look to mount a new European challenge in the EPCR Challenge Cup Round of 16.
Scorers
Harlequins:
TRY: David (2), Lynagh (2), Care, Esterhuizen, Evans
CON: Smith 6
Ulster:
TRY: McCann, McCloskey, Stockdale
CON: Cooney, Doak
Ulster:
(15-9)Lowry (Addison); Baloucoune, Hume(Marshall), McCloskey, Stockdale; Burns, Cooney (Doak);
(1-8) Kitshoff (Warwick), Stewart(Andrew), O'Toole (Moore), Treadwell (Sheridan), Henderson (capt), Matty Rea, McCann (Rea), Timoney.
Replacements: Andrew, Warwick, Moore, Sheridan, Rea, Nathan Doak, Marshall, Addison.
Harlequins: Green; David, Beard, Esterhuizen, Anderson; Smith, Care; Marler, Walker, Collier, Herbst, Hammond, Cunningham-South, Evans, Dombrandt (capt).
Replacements: Riley, Baxter, Lewis, Launchbury, White, Porter, Anyanwu, Joseph.