A last minute goal from David Robertson ended Rangers' dreams of a treble after Dundee United won their Scottish Cup quarter-final replay 1-0 at Tannadice on Wednesday.
Goalkeeper Allan McGregor was at fault as he rushed out of goal to block Robertson's initial shot but the ball ricocheted off him and back off the United player and trickled into an empty net. United, who had lost 7-1 to Rangers in December, dominated the match and will now meet Raith Rovers for a place in the final with Celtic facing Ross County in the other semi-final.
Rangers manager Walter Smith was unhappy to lose the game right at the death. "I don't think we deserved to lose it as we put a lot into the game tonight," the Rangers manager said. "It was a hard-fought game and I'm just a little bit disappointed to lose it at the end in the manner which we did."
Dundee United manager Peter Houston said his side had come a long way from their mauling in December. "We showed great character and resilience to come back to 3-3 in the first tie but this is a massive win for the club," the United boss said. "It's a wonderful opportunity for us and I'm delighted for the players."
Rangers may have lost out on the treble but their chances of winning the title improved immeasurably as arch-rivals Celtic were astonishingly thrashed 4-0 by St Mirren in a Premier League clash. Doubles from Andy Dorman and Steven Thomson gave St Mirren their incredible winning margin, to leave Celtic ten points behind their rivals, who have two games in hand, and piles the pressure on manager Tony Mowbray.
At Tannadice Rangers made seven changes from the side that clinched the League Cup on Sunday with Kris Boyd and Kenny Miller dropping to the bench with rare starts for Andrew Little and John Fleck. A more familiar looking Dundee United made a flying start when Jon Daly forced McGregor into a save and Craig Conway fired just wide in the opening minutes.
Fleck's mazy run ended with his shot cannoning off a United defender's legs before Mihael Kovacevic's dipping volley bounced inches wide of McGregor's post. United then had a trio of penalty claims turned down by referee Dougie McDonald, who awarded Rangers two spot-kicks in their first attempt at the tie at Ibrox ten days ago.
It took until the 73rd minute for Rangers to have a shot on target when Little connected with DaMarcus Beasley's cross but Dusan Pernis, who had been a virtual spectator until then, easily saved his weak effort. Nacho Novo set up fellow substitute Kenny Miller but Pernis was equal to his drive before McGregor's mistake in the 90th minute allowed Robertson to fire United into the semi-finals.
In Paisley Celtic had the majority of chances with Georgios Samaras and Robbie Keane coming close before a poor clearance from Edson Braafheid landed at the feet of Dorman on the edge of the box and he lashed a fierce shot past Lukasz Zaluska. Things got worse for the Hoops in the second-half when two Thomson goals either side of Dorman's second completed the rout and banished the memories of their League Cup final defeat on Sunday.
Mowbray - who succeeded Gordon Strachan last summer and promised to shake up what he viewed as a stale squad while still challenging Rangers - refused to be drawn on the fans' reaction after the game but said he would shoulder the blame for the defeat. "I'll take responsibility for the way we played tonight and maybe we need to play a different set-up away from home," Mowbray said.
"We went chasing the game and left some young defenders exposed and vulnerable. I take responsibility for making attack-minded substitutions to get back into it and they made us pay."