Hull (22) 26
Tries: Lee, Briscoe, Hall 3 Goals: Tickle 3
Harlequins (0) 6
Tries: Sharp Goals: Purdham
Craig Hall's hat-trick saw Hull recover some lost pride and put a serious dent in the play-off hopes of Harlequins.
Tommy Lee pushed through for a fifth-minute try, which was quickly followed by another from Tom Briscoe.
The visitors, now with one win in 10, failed to cope with Hall, who scored his tries - all converted by Danny Tickle - within a 15-minute spell.
Will Sharp responded with a 67th-minute try but Hull snuffed out a fightback to register their 10th league win.
Quins will now need other results to go for them over the remainder of the weekend to keep their play-off hopes alive.
Hull coach Richard Agar:
"I thought there was some good stuff in there - we built up a good lead and we got the job done scoring some nice tries along the way.
"We didn't set them too many parameters before the game, just play with your head up and play to the space.
"Craig Hall is a classic centre. Some of the tries he scored were classic centre play.
Harlequins coach Brian McDermott:
"I just said to them that while ever they've got that inner steel about them, we're in good nick. We're not the smartest team but as a group of people we're pretty strong.
"I think our form was more of a concern. I don't see that as a chance missed, our play-off chances started crumbling three, four, five weeks ago.
"Momentum is a funny thing. We started to lose a bit when we had some injuries. Just as they start coming back we don't seem to have the momentum."
Hull: Whiting, Calderwood, Briscoe, Hall, Raynor, Washbrook, Tansey, Dowes, Dowes, Lee, Cordoba, Manu, Tickle, Radford, Houghton, Moa, Lauaki. Replacements: G. Horne, Lauaki, Moa, Houghton, Lee.
Harlequins: Melling, Wells, Gafa, Purdham, Sharp, Dorn, Gale, McCarthy-Scarsbrook, Randall, Heckenberg, Golden, Bryan, Williamson, Orr, Kaye, Ward. Replacements: Sharp, Orr, Bryan, Heckenberg, Kaye, Ward, Randall.
Referee: P Bentham (Warrington).