Bent headed home after strike partner Richard Naylor had hit the bar, at the end of a week in which he was questioned by police over an alleged air gun incident.
Ipswich began well and Tomas Repka had to make a good block to deny Bent when a Jim Magilton corner fell to him after six minutes.
Marlon Harewood had the ball in the net on 11 minutes, but the whistle had already blown for a foul, and a minute later, he wasted a good chance, firing into the side-netting.
Magilton had a low drive deflected wide before his cross found Bent whose hooked shot was grabbed by Stephen Bywater at the second attempt.
Bobby Zamora and Bent both struck weak efforts when well-placed, before Bent rounded Bywater and pulled the ball back to Ian Westlake, whose volley was cleared off the line by Andy Melville.
Zamora wasted two more good chances, dragging one effort wide and then tamely shooting straight at Kelvin Davis.
The last good chance of the half saw Jermaine Wright volley just wide from a Magilton corner.
West Ham had the first chance after the break, Harewood heading a Michael Carrick corner on to the roof of the net.
Bent shot over from a Westlake cross before netting his potentially priceless goal, heading home from six yards.
Bent curled an ambitious effort over soon afterwards and that was Town's last real threat.
Both sides seemed happy to take the result, although both Carrick and David Connolly brought saves out of Davis before the end.
Like the other Nationwide Division One play-off semi final, nothing has been resolved, but Ipswich will be the happier of the two teams, knowing just a draw on Tuesday will take them to Cardiff for the final.