Dundee United manager Craig Levein believes his side have failed to reach their potential after St Mirren's 1-0 Scottish Cup fifth-round replay victory at Tannadice.

Andy Dorman's 48th-minute goal settled the tie and set up a last-eight clash with St Johnstone at McDiarmid Park on March 8.

United have endured a productive season thus far, currently sitting third in the Clydesdale Bank Premier League, while they will play Rangers in the CIS Insurance Cup final next month.

Therefore Levein believes his side should have been able to not only defeat St Mirren but to reach the latter stages of the tournament.

"The disappointment for me is that I know we were a good enough team to progress quite far in this competition this year," he said.

St Mirren took the game to United right from kick-off, with Christian Kalvenes required to block a goal-bound Craig Dargo shot after little more than 10 seconds.

Dargo should then have broken the deadlock when home goalkeeper Lukasz Zaluska's bizarre attempt to keep the ball in play resulted in him releasing it from his grasp on the touchline.

The former Inverness striker took possession of the loose ball with glee but could only shoot wide from an acute angle when he should have done far better.

Nevertheless, Levein thinks just being able to create those squandered goalscoring opportunities gave St Mirren a big boost.

He said: "We didn't start particularly well which I think that gave St Mirren a lift.

"They had a couple of chances early on in the match that they didn't have to work very hard for."

St Mirren finally broke the deadlock when Dorman latched on to a Dargo header and provided a confident finish.

Levein insisted Dargo was offside prior to playing the ball, but thought Lee Wilkie could have done more to try and prevent the goal.

He said: "Wilkie has to take a certain amount of the blame because he is an experienced player.

"He put his hand up to play offside and stopped rather than continuing his run.

"I don't think he would have got the ball any way but the fact is he could have kept playing."

St Mirren had to rely on goalkeeper Mark Howard - starting in place of Chris Smith who is undergoing hospital tests for a potential gland problem - producing an excellent late save from a spectacular Noel Hunt overhead kick.

However, manager Gus MacPherson believes his players were still worthy winners.

"We played well, we thoroughly deserved to win and we are delighted with that," he said.

More news from SportingLife.com