Rangers have been knocked out of the Scottish Cup 2-0 by Dundee United on Sunday at Ibrox.
Goals from Gavin Gunning and Johnny Russell proved the difference as Dundee United reached the quarter-finals.
The match was the Gers' first since the deadline day sale of top scorer Nikica Jelavic to Everton, and the Croatian's absence was sorely felt when faced with a stubborn rearguard action from the visitors.
Dundee United soon had the goal their spirited opening deserved, with Gunning powerfully heading the ball beyond McGregor with just over a quarter of an hour played.
The Scottish champions poured forwards in search of an equaliser, bombarding the Dundee United defence with crosses.
But the visitors dealt with the flank assault well, although David Healy forced a superb save from Dusan Pernis with a low shot.
But without Jelavic, Rangers lacked any real cutting edge up front and, having weathered the storm, the visitors then doubled their lead 10 minutes before the interval.
Some slack defending afforded Russell too much space in the penalty area, and the striker gleefully slammed the ball past McGregor.
Now presented with a minor mountain to climb, the hosts attacked with greater urgency, but not necessarily with greater threat, and Dundee United carried their two-goal lead into the break.
From the start of the second period Rangers resumed their relentless attacking pressure, pinning their opponents inside their own half and probing for a way through.
But Dundee United continued to defend stoutly, and as their frustration grew Rangers found more yellow cards coming their way than clear chances.
Substitute Andrew Little wasted their best opportunity when he lashed wide from an inviting Aluko cross, while the visitors spurned numerous presentable counter-attacking opportunities to make the game safe.
Rangers battled gamely until the whistle, but the comeback never looked likely, and Dundee United held on to secure a famous upset.