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Dundee United secured a Scottish Cup final place with an opportunist, but ultimately comfortable, victory over Rangers.

Stuart Armstrong finished decisively for the opening goal, which came after the Ibrox side spurned a clear chance.

Gary Mackay-Steven's second came via a deflection and the Rangers goalkeeper Steve Simonsen made an error for Nadir Ciftci's third.

The Ibrox side had made it 2-1 with a first-half Steven Smith free-kick.

But they were unable to truly threaten United's passage to a final meeting with either Aberdeen or St Johnstone on 17 May.

Whoever Jackie McNamara's side face, the occasion is likely to lack the relentless intensity of this contest.

Interview - Dundee United boss Jackie McNamara

The game initially had to accept second billing, since the competition was between the two sets of supporters and their goading of each other. The noise spilled from the Ibrox stands as if oblivious to events on the pitch.

There was soon a hectic urgency to the play, though, and composure was an early victim of the heightened atmosphere. There were pent-up emotions to be released, and the quality of the game suffered from the raucous surroundings.

There was excitement and zeal as the two sets of players hared around the Ibrox pitch, but not enough self-control to bring some poise to the proceedings.

Rangers had the most cause to rue that lack of restraint, since they should have opened the scoring when Dean Shiels was sent through on goal. The forward hurried his finish, though, and scuffed the ball wide.

It became a galling miss for Rangers, because minutes later a hopeful Gavin Gunning header sent Armstrong clear.

Nadir Ciftci was returning from an offside position but was deemed not to be interfering with play and Armstrong took advantage of the confusion to clip a shot past Simonsen that kissed a post before nestling in the net.

A pattern was established, since Rangers had the better patches of play, but could not influence the outcome.

Armstrong (left) beat the offside trap to put United ahead

When Fraser Aird was free in the area, he laid the ball back to Jon Daly, only for the striker to direct a shot rashly over the bar.

Moments later, Richard Foster failed to clear his lines and allowed Ryan Gauld to burrow into the Rangers penalty area before shunting into the path of Armstrong. He could not connect cleanly and neither, subsequently, could Mackay-Steven, but the ball looped off Bilel Mohsni, over Simonsen, and into the net.

Smith restored some hope for Rangers with a free-kick that squeezed between Radoslaw Cierzniak and the base of his left-hand post.

That goal came just before half-time and, athough Rangers continued to enjoy greater possession after the interval, their frailties could not be disguised.

Mohsni was often hapless in possession, attacks were intermittent and haphazard in nature, and there was not enough link-up play between the midfield and the forwards.

United's midfield struggled to retain possession, and their defence often sat too deep, but their four front players were a constant threat, not least because of the calamities that the Rangers defence were capable of.

When Foster broke up one move and passed back to Simonsen, the goalkeeper hesitated before stubbing the ball straight at Ciftci. The striker rounded the stricken goalkeeper and was celebrating even before he rolled the ball into the empty net.

Rangers restored something of their reputation with this display, but United were the more clinical side.