The Warriors were the better team in the opening exchanges, shocking the home side with tries from Bryan Fletcher and Chris Ashton putting them into the driving seat and opening up a 10-0 lead.
Vainikolo was at the forefront of a Bradford fightback, combining with Shontayne Hape for his first and powering through the Wigan defence for his second, before Glen Morrison grabbed a touch down to put the Bulls 18-10 up.
Terry Newton was the first to score following the half-time interval, and Vainikolo completed his hat-trick after touching down David Solomona’s grubber into the in-goal area to give Bradford a commanding 30-10 lead.
Former Bulls player Stuart Fielden touched down for two well worked tries against his old club as the Warriors fought back, but this was not enough for the visitors to get back into the game.
Bradford had enough in defence to hold out, and Paul Deacon converted a penalty in the final moments to seal the win for the Bulls.