It was a game which they had virtually controlled from start to finish, but they missed a hatful of chances as they allowed the visitors to steal a point.
The hosts began slowly, taking ten minutes to carve out their first chance when Noel Hunt thundered Sean Dillon's cross off the body of Will Haining - an excellent block by the defender.
The chance was followed by two opportunities in quick succession, most notably one for Mark De Vries who took too long from only a yard out.
A marvellous drive from Willo Flood in the 22nd minute then almost split the crossbar. Such was the ferocity of the shot that the ball spun into play and bounced back over the bar.
While United were strong going forward, they were equally poor in defence with another mistake by Dillon allowing Craig Dargo to cut the ball back for Mark Corcoran but he finished with too much haste.
In the 34th minute, excellent work by Danny Grainger set up De Vries but a poor finish prevented him breaking his Tangerines duck as he headed wide with the goal at his mercy.
Morgaro Gomis then got involved in the action with a powerful low shot that was arrowed at Mark Howard.
The second half almost started with a bang as Howard booted a clearance off the onrushing Hunt, but fortunately for the Buddies keeper, it rebounded narrowly wide.
United continued to dominate and Hunt went close five minutes later with a header which flew off Haining but somehow Howard tipped the ball over the bar.
St Mirren's first real chance came in the 61st minute when Andy Dorman's cross flew off the thigh of Dargo but was well-saved by Lukasz Zaluska.
In the 68th minute, it appeared as though United would find the net when a neat touch by Hunt set up substitute Jim O'Brien but somehow Ian Maxwell blocked his effort.
Dundee United's pressure was eventually rewarded a minute later when a deep cross was met by Dillon who ghosted in at the far post to volley low past the despairing Howard.
But United were to pay for all their missed chances when, two minutes from time, Dorman stole in for the equaliser when he latched on to a missed clearance by Darren Dodds to stab the ball home from eight yards.