As United celebrated their victory in front of 11,000 boisterous 'Arabs' they also subjected Ally McCoist and Rangers to yet one more painful setback.
With McCoist these days, his job security is the elephant in the room.
The Rangers manager can take some comfort from his team's gritty play today, though that might be his only consolation. McCoist is a manager surrounded by doubters, at a football club which, on and off the field, appears in perpetual disarray.
Rangers have played far worse than this under McCoist, though his record in cup competitions since becoming Rangers manager is atrocious. His increasing critics are noting it. Some had even believed this cup semi-final would be a defining moment for him.
In truth, there can be nothing definitive about today's events for McCoist, with his club's off-field pageant in part shielding him. It seems likely he will soldier on as Rangers manager until such times as boardroom solidity and clarity prevail.
Perversely, Rangers played far better against United than they have done all season, with skill and urgency underpinning much of their football. McCoist's defence, however, looked feeble at this level, with Bilel Mohsni a walking liability.
When they needed to, Dundee United sliced Rangers open, or were sometimes just invited to walk through them. United can play far better, but there was still much calm intelligence about a lot of their work.
An oddity of this game and its outcome was that, while Rangers were trailing 2-1 at half-time, they might easily have been leading 3-2. In this context McCoist could glean some comfort in showing that he could coax a gritty and menacing performance from his players - a frequent omission this season.
Dean Shiels and Jon Daly both fluffed chances with only Radoslaw Cierzniak to beat, though Dundee United, when it was required, revealed their own trickery and menace.
McCoist's post-match musings were of how much he believed Rangers had been the better team, though one comment he made seemed to cut to the quick and begged a huge question of his managerial ability.
Believing his team had matched and indeed bettered United, McCoist said: "This has just confirmed what I've thought all along - I reckon we are a team of top-flight ability."
In which case, why have Rangers under their manager subjected their supporters to such frequent, abject football?
Off the pitch, the political wrangling over the Ibrox club continues, with Dave King again leading the charge to oust the current Ibrox board via a ramped-up publicity campaign and a proposed new share-issue.
It has become a very bitter dispute. There is claim and counter-claim aplenty, and accusations of "liar" being flung by all and sundry over what either King or the board have reputedly previously stated.
For the broad Rangers support, already wrung dry by events of the last two years, it is a painful choice once more of whom to believe.
King is requesting a withholding of season-ticket money by supporters, an act that will undoubtedly hurt the club, and will cause many Rangers fans to bridle. Other supporters, however, especially those found among Rangers' social media activists, are vehement in their support of King.
For most of them, King's recent court conviction in South Africa for illegal tax affairs is an irrelevance, a non-story. King is reputedly rolling in it and his moral background in business doesn't enter the equation. These supporters want his money, pure and simple.
The next bout of dispute will arrive when Rangers CEO Graham Wallace announces his financial review of the club, which is due over the next seven days. If the heat is on McCoist, it is also on Wallace.
His case - and that of his embattled board - will look weak unless he can promise improvement in Rangers' financial position and show a capacity to find fresh investment in the club. If that doesn't come, King and his supporters will erupt once more.
Another bad day for Rangers. And in his 2013-14 season, surely not the last.