Steven Thompson netted his first competitive goal for the Buddies after 11 minutes with a neat finish from close range to give them a half-time lead over his former club.
However the visitors were reduced to 10 men in first half injury-time when Nigel Hasselbaink was dismissed for catching United defender Paul Dixon with his arm.
Jon Daly levelled after 67 minutes after turning home a Scott Allan cross but, despite their second half dominance, the Terrors were unable to find a winner.
United, who were without Danny Swanson through a virus and departed striker David Goodwillie, stuck with the same side that defeated Hearts 1-0 last weekend.
St Mirren, who received plenty of plaudits for their attacking displays against Dunfermline and Aberdeen, also named an unchanged starting XI from the side that ran out 1-0 winners over the Dons.
United suffered an early setback when defensive midfielder Scott Severin was carried off on a stretcher after coming off second best in a robust challenge with Buddies skipper Jim Goodwin only a couple of minutes into the match - he was replaced by Scott Robertson.
And things went from bad to worse for the hosts when the Buddies took the lead after 11 minutes.
Hasselbaink showed great trickery down the left wing to evade the challenges of two United defenders before finding Thompson at the near post,
who prodded the ball home from close range.
The lively Hasselbaink showed great skill once again to jink past Garry Kenneth after 15 minutes but this time his left-footed shot at goal was gathered by United stopper Dusan Pernis.
United should have squared things after 27 minutes when St Mirren's Craig Samson could only parry Kenneth's powerful free-kick into the path of Keith Watson - but the full-back completely missed the ball with the goal at his mercy.
St Mirren continued to impress with former Celtic youngster Paul McGowan seeing his dipping long-range effort tipped over by Pernis for a fruitless corner just before the break.
The half ended in controversy when Hasselbaink was given a straight red card in the fifth minute of injury-time after catching Paul Dixon with his arm when running in on goal.
United came out for the second half determined to get an equaliser with Willo Flood's deep corner dropping kindly to John Rankin - but Darren McGregor made a desperate block to thwart the former Hibernian midfielder.
Johnny Russell was the next player to try his luck, with Samson equal to his diving header, before the striker drilled a left-footed strike inches past the upright.
The home side went even closer on the hour mark when Watson's cross into the area was met by United skipper Daly - but the Irishman's header just brushed the wrong side of the post.
But the inevitable equaliser arrived after 67 minutes when the impressive Scott Allan darted down the wing and rounded Goodwin before picking out Daly, who turned the ball home at the near post.
United looked the more likely to go on and win the match but Samson pulled off a tremendous stop to claw away an Allan drive through a ruck of players.
However the Buddies bravely held on for a point to continue their unbeaten start to the season.