A howler from Rangers stand-in 'keeper Steve Simonsen sealed Dundee United's place in the Scottish Cup final following a 3-1 win at Ibrox on Saturday.

Rangers had chances through Bilel Mohsni and Dean Shiels before Stuart Armstrong fired United in front in the 23rd minute.

Jon Daly should have had Rangers level before a deflected shot from Gary Mackay-Steven made it 2-0 in the 36th minute.

Nicky Law hit the bar and then Steven Smith pulled one back for the fallen Glasgow giants with a 42nd-minute free-kick that Radoslaw Cierzniak fumbled in.

Rangers pressed for an equaliser in the second half but an horrendous attempted kick out from Simonsen eight minutes from time allowed Nadr Ciftci to make it 3-1.

It is the fourth time in the past five seasons United have knocked Rangers out of the competition and the sixth straight cup tie they have won against the Ibrox club, who were hoping to make their first major final since 2011.

However, United manager Jackie McNamara was delighted to see his side progress to the final.

"I think for everybody connected with the club it is a great feeling to get to the final and it gives us something to look forward to at the end of the season," McNamara said.

"I think we can play a lot better than we did today, especially in the second half, but we're just delighted to be there."

In contrast, Rangers manager Ally McCoist was bitterly disappointed at his side's missed chances.

"I thought we were the better team for the majority of the game but just poor decisions cost us," McCoist said.

"I thought we slit our own throats with the goals we lost and our level of finishing wasn't what it should be as we definitely had some great chances to score today."

Rangers were without Lee Wallace and David Templeton following injuries in last weekend's shock defeat by Raith Rovers in the final of the Challenge Cup - the knock-out tournament for lower-league clubs - while regular 'keeper Cammy Bell was replaced by Simonsen after suffering concussion in training.

Two divisions separate the sides following Rangers' drop to Scotland's bottom tier after liquidation in 2012 but the lower-league team had the huge advantage of playing at their own stadium and they started strongly with Mohsni's header cleared off the line by John Rankin in the third minute.

Fraser Aird was causing United real problems down the left and the winger came close as he sent a curling shot into the side-netting from 20 yards.

Shiels missed a golden chance to put his side in front when he beat the offside trap and raced clear of the United defence to collect Daly's through ball but sliced his effort wide when one-on-one with the 'keeper.

Rangers were to rue that miss four minutes later when United took the lead through Armstrong. The United midfielder kept his cool to collect a headed forward pass from Gavin Gunning and sent a hooked shot over Simonsen that went in off the post.

United hadn't been in the match until that point but could have gone two up a minute later when Ciftci forced a superb save out of Simonsen with an angled shot.

Rangers should have been level in the 35th minute when Aird got behind a static United defence to cushion an Ian Black lofted pass into the path of Daly, but the former United striker scooped his effort high and wide.

They were punished a minute later as United made it 2-0. Ryan Gauld got to the byline and cut the ball back for Armstrong, whose blocked shot landed at the feet of Mackay-Steven and his shot took a deflection off Mohsni on its way past Simonsen.

Rangers finally got the goal their efforts merited in the 42nd minute when Smith's curling free-kick went through the United wall and was fumbled in by Cierzniak.

A howler from Simonsen sealed the win for United in the 83rd minute, though. His attempted kick-out from a Ricky Foster pass-back rolled to Ciftci who rounded the 'keeper and passed the ball into the empty net.