A dramatic injury-time winner from David Robertson ensured Dundee United will face Inverness in the fourth round of the Tennent's Scottish Cup following a remarkable clash with St Mirren at Tannadice.

Barry Robson's brilliant first-half free-kick and a powerful header just after the interval from Garry Kenneth handed United a deserved two-goal lead, before Richard Brittain's penalty gave the Paisley club late hope.

John Sutton's 81st-minute equaliser then looked to have sent the tie to a replay at Love Street, only for Robertson to pounce with almost the last kick of the game to send United through.

This match was rescheduled from its original January 7 date, as United were successful in their appeal to have the fixture postponed following an outbreak of flu at Tannadice.

St Mirren thought they had turned their first attack into a goal, only for Sutton's header following a Mark Corcoran cross to be ruled out for offside.

United retaliated with a route one attack, which saw Jon Daly flick a Derek Stillie clearance into the path of Collin Samuel, who proceeded to send a dipping half-volley just wide of goal.

The Buddies then thought they should have been awarded a penalty as Alan Archibald appeared to manhandle Sutton in the home side's 18-yard-box, before Brittain pounced to fire a snap-shot marginally past Stillie's left-hand post.

As chances were traded by both sides, the Tangerines were next to threaten and Tony Bullock did well to smother Robertson's low shot on the goal-line, after Robson's inswinging corner broke to the 20-year-old in the Buddies' box.

However, the visitors' goalkeeper was then completely caught out by Robson's free-kick, as Bullock gambled on a left-footed drive being angled towards his near post, only for the ball to curl away from his dive and nestle high in the St Mirren net.

Frustratingly for the away side, in addition to the concession of that goal the key decisions continued to go against them, as Stillie appeared to gather the ball outside his area, only for referee Charlie Richmond to adjudge that no infringement had occurred.

Barely 40 seconds into the second period United scored from a strikingly simple set-piece, with Kenneth powering a header past Bullock following Conway's corner.

But St Mirren's comeback started when Kirk Broadfoot managed to goad Daly into making a mistimed tackle in the United penalty area and Brittain confidently converted the resultant spot-kick.

Within 60 seconds, the visitors came close to finding an equaliser when Alan Reid's driven cross from the right wing was somehow turned away from goal by Stillie, as Stewart Kean lurked menacingly in the six-yard box.

But with nine minutes remaining, St Mirren were back on level terms, as Broadfoot played in Sutton with an intelligent through-ball and the former Dundee striker confidently placed a right-footed shot past the cruelly exposed Stillie.

Remarkably, the Buddies almost scored a third goal in the last minute of injury-time, when Sutton barged his way towards goal and was only denied by a great save from Stillie.

But it was United who found a winner with almost the last kick of the game, as Conway crossed for Robertson to secure an amazing victory for the Tangerines, courtesy of a bouncing shot from 12 yards.

Teams:

Dundee Utd Stillie, Watson (McCracken 85), Mair, Kenneth,Archibald, Conway, Kerr, Robertson, Robson (Duff 59), Samuel,Daly.

Subs Not Used: McLean, Hunt, Goodwillie.

Booked: Daly.

Goals: Robson 31, Kenneth 46, Robertson 90.

St Mirren Bullock, Broadfoot, Millen (Kean 56), Maxwell,van Zanten, Brittain, Potter, Brady, Lappin (Reid 71), Sutton,Corcoran.

Subs Not Used: Smith, Mackay, McKenna.

Booked: Millen.

Goals: Brittain 76 pen, Sutton 81.

Att: 4,010

Ref: C Richmond (Scotland).