Craig Levein was left to rue the irony after a mistake from an official proved the deciding factor in Dundee United's cup exit to St Mirren.Levein was adamant Craig Dargo was offside when he headed the ball into the path of Andy Dorman, who provided a cool finish from close-range to beat Lukasz Zaluska.

The build-up to the fifth round replay had centred on the appointment of referee Alan Freeland, with St Mirren protesting to the Scottish Football Association at the official's involvement.

The Paisley club are believed to have taken issue with comments allegedly directed to them by Freeland when he was the fourth official during a game with Falkirk 10 months ago.

Freeland had not taken charge of a St Mirren game since, but was awarded tonight's tie when Mike McCurry, who handled the goalless draw between the sides on February 2, was unavailable.

In the end Levein had no problems with Freeland's performance, but insisted assistant referee Craig Young made the wrong call in allowing Dorman's goal to stand.

He said: "I don't think we were at our best and I still think we did enough to at least get into extra-time, but the game has been decided on a mistake by an official, which is pretty ironic.

"It wasn't the referee after all of the pressure that was on him, but you just wonder if additional pressure in that room has maybe had an affect on them.

"It is a clear offside and it is a disappointment to have lost the game in that way.

Levein added: "I thought the referee was okay and I am not in the habit of criticising officials as I have done all of that in the past.

"I don't do it anymore, but people will bring it up because it was one of the talking points before the game.

"It was an offside goal, but these things happen in football."

St Mirren manager Gus MacPherson would not be drawn on the performance of Freeland, saying: "The SFA will not allow us to comment on the referee."

He also defended his side's actions prior to the game, saying: "St Mirren Football Club haven't done anything wrong and in the last couple of days people were trying to spin it the other way."

The Buddies boss preferred instead to concentrate of a fine performance from his side, which took them through to a quarter-final tie at First Division St Johnstone on Saturday March 8.

St Mirren came close to scoring after just 10 seconds when Christian Kalvenes blocked a shot from Dargo, while the former Inverness striker should then have found the target when United keeper Lukasz Zaluska made a terrible error.

Zaluska kept the ball in play, handing it on a plate to Dargo, but his resulting shot flashed straight across the face of goal.

St Mirren eventually broke the deadlock in the 48th minute through Dorman and although keeper Mark Howard had to produce a brilliant late save to keep out an overhead kick from Noel Hunt, the Buddies ultimately secured a the win MacPherson thought their efforts deserved.

He said: "We should have made it slightly easier for ourselves, but we played some real good stuff at times and created chances against a team that is sitting third in the SPL.

"To come to Tannadice and create so many chances especially in the opening half-hour is a credit to the players."

MacPherson confirmed regular goalkeeper Chris Smith was in hospital with a potential gland problem and was scheduled to undergo tests.

More Football News from TEAMtalk