Sunderland gained the upper hand on Manchester United by deservedly winning their League Cup semi-final, first leg 2-1 on Tuesday to intensify the pressure on visiting manager David Moyes after a testing week.
Italian Fabio Borini scored a second-half penalty to give the Premier League's bottom club a one-goal lead ahead of the return at Old Trafford after a 52nd minute Nemanja Vidic header cancelled out Ryan Giggs's own goal in first-half stoppage time.
It was United's third straight defeat after they were beaten at home in the FA Cup third round by Swansea City on Sunday and by Tottenham Hotspur in the league the previous week, heaping pressure on Moyes in his first season in charge.
The second leg will be on Jan. 22 to decide who will face either favourites Manchester City or West Ham United, who play at the Etihad Stadium on Wednesday, in the final on March 2.
For beleaguered United manager Moyes, the League Cup has developed added significance with the club already out of the FA Cup, looking unlikely to retain their Premier League title and long odds to win the Champions League.
For the fans who booed them off the pitch following the loss to Swansea, there was little to perk up the spirits.
This was the first time since 1932 that United had lost their opening three games of the year and the first time since 1992 that they had lost three times in a week.
Moyes blamed the officials, who he criticised for awarding Sunderland the free kick that led to the first goal, rather than his players who he described as being "unbelievable".
"It looks as though we are having to play them (the officials) as well as the opposition at the moment," he said.
"I thought the players, our crowd were unbelievable, the players deserved to get a result. It's a two-legged game and I am really looking forward to the second leg."
Sunderland have only reached the League Cup final once, in 1985 when they lost to Norwich City, and their fans do not need reminding they were relegated from the top flight that season.
The knockout competitions have again provided Sunderland with their only moments of relief in a miserable campaign, having won all five home ties in the League and FA Cups.
There were rows of empty seats at the Stadium of Light but those who ventured into the cold saw them make a bright start.
They kept possession well in the opening minutes, subduing a United side for whom exciting Belgian teenager Adnan Januzaj provided a lone attacking threat.
After Giggs rattled the bar with a dipping drive, the 18-year-old Januzaj had the ball in the net seven minutes before halftime only to be denied the opening goal by the offside flag.
In the end it was Sunderland who made the breakthrough in first-half injury time. Jonny Evans gave away a needless free kick and Seb Larsson's whipped set piece was diverted in by Giggs under pressure from former United player Phil Bardsley.
It was the first goal United had conceded in the competition all season.
The gloom among the travelling fans was briefly lifted seven minutes into the second half when Serb defender Vidic, returning to the side, drew them level with a towering far post header.
Yet it was Sunderland who displayed a resilience lacking for much of their league campaign, retaking the lead through on-loan Liverpoolforward Borini from the penalty spot after Adam Johnson had been felled in the area by Tom Cleverley.
There was no backs-to-the-wall finale and it was Sunderland, who had not beaten United in 20 matches, who looked the more likely to increase their lead, with United leaving it late before throwing bodies forward to try and force a leveller.
"It's something very strange but with the way we are playing maybe it is suited to playing against the big teams. It was a very tight game, and sometimes a decision goes for you and you win the game," Sunderland manager Gus Poyet said.
"We know it's not easy to beat Manchester United but now we go to Old Trafford with a lead. It has been a long time since we were in a final so we will try our best."