The United striker was alert to net a loose ball from close range at the end of a match in which his side had enjoyed the majority of chances.
They had fallen behind on 73 minutes when new St Mirren signing Sean Lynch marked his debut by scoring the opener following a corner.
New St Mirren manager Danny Lennon handed debuts to six new players as his side kicked off their SPL campaign.
Returning defender David van Zanten, back for a second spell at the Paisley club, started alongside Lynch, Darren McGregor, Gareth Wardlaw, Paul McGowan and Jure Travner.
St Mirren dominated the early stages and had the first effort on goal on three minutes when Steven Robb's free-kick from the right touchline reached the far post and was headed goalwards by John Potter, but it was cleared for a corner.
Wardlaw then won a long ball forward despite the attentions of Kenneth and tried a turn and shot from a wide position, but his effort never troubled visiting goalkeeper Dusan Pernis.
Centre-half Darren Dods headed onto the roof of the net from a Craig Conway free-kick after the midfielder himself had been brought down just outside the left edge of the box.
Conway then sent in another searching free-kick on 20 minutes which was met at pace by Garry Kenneth at the right-hand post, but home goalkeeper Paul Gallacher kept out his header.
United consistently pressed around the St Mirren goal for the remainder of the half, coming ever closer to a goal.
Morgaro Gomis tried his luck with a speculative shot from distance, but it went over the bar, and Prince Buaben then tried a strike which went past the left-hand post.
In between, St Mirren had a penalty appeal turned down as they felt Paul Dixon had handled in the box.
Kenneth again found his way into the box to try his luck following a Conway corner as the visitors continued to unleash a series of set-pieces around Gallacher's goal as the interval approached, including a free-kick from the midfielder which went narrowly past the post.
David Goodwillie had the first half-chance after the restart, but Gallacher rushed out to smother at the striker's feet.
At the other end, Steven Robb fired in a cross from the left touchline which Pernis appeared to have under control, but it ended up hitting the corner of the woodwork before being claimed by the goalkeeper.
United had their nearest miss yet on 51 minutes when Conway escaped Van Zanten to cross for Goodwillie, but the striker's header sneaked just wide.
Gomis then had a half-volley following a corner booted away from the right-hand post by Robb as United continued to dominate.
Daly ended up on the deck in a busy box as he and Van Zanten jostled for position for Gomis' cross from the right; and the United striker had a glancing header touched narrowly out for a corner moments later.
Gallacher was again called into action on 69 minutes as Gomis threaded a pass to Daly who cut inside two defenders before curling a shot which the goalkeeper stretched to touch over.
Despite United's pressure, however, it was St Mirren who finally broke the deadlock four minutes later - a corner from the right arrived at the feet of Lynch and he unleashed a volley which soared past Pernis and into the top right corner of the goal.
United looked to respond and Conway sent in a promising cross but Daly was unable to connect with his diving header.
However, the striker netted a deserved equaliser by following up a shot which had been blocked by Potter to slam home from six yards.