JOHN SUTTON reckons St Mirren's fighting spirit should have been enough to keep their Scottish Cup dreams alive.

The Paisley side crashed out of the competition in dramatic fashion as an injury-time goal handed Dundee United a 3-2 victory in the third round clash at Tannadice.

After falling behind to goals from Barry Robson and Garry Kenneth, Saints looked to be dead and buried until Kirk Broadfoot won a penalty kick decision which Richard Brittain made no mistake with.

And when Sutton netted the equaliser it looked as though Gus MacPherson's men had managed to survive to fight until day - until a defensive error deep into injury time handed David Robertson the winner.

It was a sickening way to lose the tie and the big Englishman admits the manner of the defeat was hard to take.

He said: "I thought we showed great character to come from two goals behind to get back on level terms.

"Instead of letting the heads go down, we just got the sleeves rolled up and got on with it. The penalty kick award which Richard Brittain converted gave us hope and I managed to equalise when I was put through on goal.

"At that stage you've got to be happy with a draw and taking the game to a replay, especially after being two behind.

"And it looked as though that was going to be the case up until United scored in injury time.

"It was a major blow because all our hard work counted for nothing in the end. I honestly believed we had done enough to merit a replay at Love Street."

Saints will concentrate on SPL survival now that their interest in both domestic Cup competitions is over.

And Sutton added: "We must make sure we pick up enough points to remain in the top flight for next season."

It was a shocking mistake from goalkeeper Tony Bullock that gifted United the opener.

As Barry Robson struck his free-kick, the keeper took a big step to his right before trying to get back in position, but he never recovered and the ball flew past him into the middle of his goal.

And after the break Broadfoot allowed Kenneth to win his header just yards out - although it was so close to Bullock that the keeper should have dealt with it.

But Brittain's penalty and a cool finish from Sutton looked to have forced this one to a replay until John Potter tried to shield the ball out of play inside his work before United stole position and Robertson found the back of the net.

Saints boss MacPherson said: "It's very disappointing to lose the game after working so hard to get back into the match and recovering from a bad start.

"Our decision making just wasn't good enough. I don't think we played well and it wasn't the greatest of games, but it's a sore one for us."