Vainikolo, who will switch codes when he joins Gloucester in July, has now scored 17 tries in 16 appearances this season and 147 tries in 148 games during his Bradford career.

He crossed twice in the first half as Bradford built up a 22-0 half-time lead and completed his treble following good work from Michael Platt inside the final quarter.

Harlequins were hit by an early blow when a shoulder injury forced Daniel Heckenberg out of the action after just six minutes.

It was the start of a miserable afternoon for the visitors, who were soon trailing in an error-strewn first half.

Vainikolo opened the scoring by barging through Tony Clubb's attempted tackle and 10 minutes later he plundered his second try in similar circumstances after Glenn Morrison's offload.

A series of mistakes combined with Paul Deacon's smart kicking game kept Quins pinned in their own half and Bradford took full advantage.

Ian Henderson's clever pass from dummy half allowed prop Joe Vagana to crash over for his second try of the season.

Then Sam Burgess broke free before slipping a well-timed pass to Deacon just before the break.

Quins could have scored soon after the restart, only for Lee Hopkins' effort to be ruled out for a forward pass.

Instead, the hosts stretched their advantage ever further as Glenn Morrison broke free.

Five minutes later Henderson dived on a loose ball in the corner to keep the scoreboard ticking over but Quins managed to regain some pride when Jon Wells, their veteran winger, touched down.

Chad Randall also crossed and Paul Sykes intercepted Iestyn Harris' pass but Vainikolo's third meant there was never any chance of a comeback.

Bulls' youngster Richie Hawkyard marked his home debut with a try to complete the scoring

Bradford:

Platt, St Hilaire, B. Harris, Evans, Vainikolo, I. Harris, Deacon, Vagana, Henderson, Lynch, McKenna, Solomona, Morrison.Replacements: Hawkyard, James, McAvoy, Burgess.

Harlequins RL:
Melling, Wells, Sykes, T. Smith, Clubb, McLinden,Orr, Temata, Randall, Heckenberg, Worrincy, Hopkins, Gafa. Replacements: Rinaldi, Mills, A. Smith, Burgess

Bulls tries:
L Vainikolo 3, P Deacon 1, J Vagana 1, I Henderson 1, G Morrison 1, R Hawkyard 1,

Bulls goals:
P Deacon 6

Quins tries:
Wells 1, P Sykes 1, C Randall 1,

Quins goals:
P Sykes 3,