Louis van Gaal was served a timely reminder of the size of the re-building job facing the club's next manager as Seb Larsson's first-half goal secured Sunderland a 1-0 victory at Old Trafford on Saturday.
The result relegated Cardiff and Fulham while drastically improving Sunderland's survival chances and leaving United with a mountain to climb if they are to finish sixth in the Premier League and secure Europa League football next season.
Defeat also handed caretaker Ryan Giggs a harsh lesson in the unpredictable world of management and suggested his predecessor David Moyes may not have been solely to blame for the club's painfully obvious current flaws.
The result also meant United, who are expected to appoint van Gaal as their new boss next week, had lost seven home league games in a season for the first time since the 1973/74 campaign, which ended with their relegation from the old First Division.
By contrast Gus Poyet's Sunderland side continued an extraordinary run which had brought a draw at Manchester City and victory at Chelsea in recent weeks after Larsson volleyed home on the half hour at Old Trafford.
Victory left the north-east side three points above the relegation zone with two games remaining.
Connor Wickham, the goalscoring hero of Sunderland's charge to safety, set up the goal with strong play at the right-hand corner flag and a cross which beat Darren Fletcher on its way to Larsson, who had slipped his marker Michael Carrick.
The Sunderland midfielder then produced a perfect 12-yard volley which flew past the diving David de Gea into the bottom left-hand corner.
It was a stunning development after the enthusiasm and support Giggs had enjoyed since taking over from sacked manager Moyes and winning his opening game 4-0 over Norwich last week.
But with Wayne Rooney missing because of a groin injury, and Robin van Persie on the bench, United were lacking a killer touch in and around the Sunderland penalty area.
Carrick's right-wing curling cross after 16 minutes almost led to a goal but it was from Sunderland's former United defender John O'Shea who sliced a clearance just wide of his own net and the right-hand post.
Juan Mata had a sight of goal on the stroke of half-time but his long shot was smothered easily by Sunderland goalkeeper Vito Mannone.
Upon the restart, Lee Cattermole's timely clearance denied Javier Hernandez a clear scoring opportunity as he shaped to convert an Evra cross with Nemanja Vidic powering a header wide from the corner that followed.
Giggs introduced Adnan Januzaj in an effort to add bolster United's play in the final third of the pitch and the move brought about an improvement with Wes Brown required to assist Mannone after the keeper fumbled a Young corner.
Another corner, this one from Januzaj himself, also culminated in Phil Jones eventually chipping to the far post, from where Sunderland cleared.
Giggs had seen enough and, after 66 minutes, made the most audacious move yet of his brief tenure as United manager, bringing on Danny Welbeck and van Persie, making his first appearance since mid-March, in place of Young and Mata.
However, it was the visitors who should have scored the next goal as Santiago Vergini swung at Jozy Altidore's cross and produced a shot which struck the foot of the United post, with Jack Colback striking the rebound into the side-netting.
Van Persie gave United fans brief hope with a half-chance at the near post which he failed to get on target, Welbeck cut in for an 18-yard shot which cleared the bar and Hernandez shot disappointingly over, unmarked from 12 yards, after being picked out by Evra's cross.
United were then almost caught on a classic counter-attack as Fabio Borini curled an impressive attempt over de Gea but onto the crossbar, with Santiago Vergini hurrying his follow-up effort over the goal from the rebound.– AFP