United haven't won at Portman Road since March 1975 and that looked like continuing when Jimmy Juan curled home a fine free-kick on 54 minutes.
However, Danny Webber conjured an equaliser, racing clear on 77 minutes, rounding Shane Supple and somehow firing his low drive home despite Town having two defenders back on the line.
The first half had been a quiet, evenly-contested affair with little in the way of clear-cut opportunities at either end.
Webber sent in an early dangerous cross flashing across the face of goal before Scott Barron's miscued cross dropped not far beyond the far post of Paddy Kenny.
A spell of United pressure saw Chris Armstrong slash a volley wide and then Jason De Vos cut out a low Paul Ifill cross from his own goalmouth.
The chance of the half almost came on 27 minutes when Webber's low cross from the right looked to be heading for Armstrong to tap in, only for Gavin Williams to get back and clear.
Kenny saved an early Darren Currie shot in the second half before Ipswich went ahead when Juan curled a 25-yard free-kick in off the crossbar after Phil Jagielka's high foot had caught Ian Westlake in the chest.
Town could have made it two five minutes later when Currie played in Owen Garvan down the left and his low cross was heading for Alan Lee on his Ipswich debut, only for Leigh Bromby to clear.
Jagielka sent a shot wide as United tried to rally and a Michael Tonge shot was deflected through to Supple, while a low shot from Town sub Danny Haynes was easily gathered by Kenny.
Town had a great chance on 65 minutes when Haynes got through on to a long clearance from Supple, but he poked his effort wide with only Kenny to beat.
Neil Shipperley headed over a Derek Geary cross before United sent on Steve Kabba in place of Ifill, with Kabba having scored both goals in United's 2-0 win over Town at Bramall Lane in September.
Lee fired an angled volley well off target for Ipswich before David Unsworth, an Ipswich loanee last season, produced a superbly-timed last-ditch tackle to deny Haynes the chance to get on to a clever Juan ball through the middle.
That proved crucial when, three minutes later, United levelled as Webber fired in from Tonge's pass with Barron and Richard Naylor unable to keep it out.
Both teams then had chances in the final seconds as Currie's free-kick from the touchline into a dangerous area was well claimed by Kenny, just in front of Lee.
Kenny immediately launched the ball forward, and although Kabba was outnumbered two to one, he won the ball, accelerated beyond Sito Castro and fired a low angled drive which narrowly beat the far post.