Sunderland, who were sixth in the league in October, went into Tuesday's game two places above the relegation zone with their last win coming against Arsenal in November.
They got off to a flying start when Fraizer Campbell scored after 41 seconds and Bent's second-half treble settled it.
His first came after 64 minutes when the striker cut inside to shoot home. He was then shoved over by Sam Ricketts for a penalty 10 minutes later which he dispatched himself .
Ricketts earned a second yellow card for the offence and was sent off and a forgettable night for Bolton, who had won their previous two games but now drop below Sunderland to 14th, was completed two minutes from time when Bent swept in his third.
Birmingham gained a measure of revenge for their 2-0 FA Cup quarter-final defeat with an easy win against a Portsmouth side who struggled to reproduce the attitude that took them into the semi-finals.
Cameron Jerome ran through to fire Birmingham ahead after 16 minutes and banged in the second shortly before halftime after a clever backheel by Christian Benitez.
Nwankwo Kanu glanced in his first league goal of the season in injury time for a consolation for the bottom club.
