A late extra time strike from Eric Djemba-Djemba killed off Leeds United's hopes of a morale-boosting victory amid frustrating scenes at Elland Road.
The Cameroon international fired in after 117 frenetic minutes to finally seal a place in the Carling Cup fourth round for Manchester United and break Leeds's hearts.
It was somewhat cruel on the home side who, after leading for much of the second half, had at least looked destined for a penalty shoot-out.
Defender Roque Junior was their unlikely hero as he scored twice ,but his efforts were ultimately not enough.
Frenchman David Bellion sent the game into extra time and Diego Forlan tapped in to make it 2-1 in the 107th minute.
The crucial and stylish winner came just minutes before the end following Junior's second goal.
Manchester United manager Sir Alex Ferguson may have fielded a weakened team for the evening, but those players who were on parade certainly had a point or two to prove in a rare first team outing.
In all the champions' manager made seven changes to the side which had won 1-0 at Elland Road in the Premiership a matter of 10 days previously.
The stand-ins, however, still made life tough for the home team.
Leeds themselves made a number of changes with Dominic Matteo, Mark Viduka, David Batty and Jermaine Pennant all missing.
Their absence enabled the returns of Roque Junior, Lamine Sakho, Ian Harte and Michael Bridges.
While there was no doubting the eagerness of either set of players the quality of the game, the first half in particular, was at times poor.
Goalscoring chances were at a premium. Salomon Olembe, playing in the heart of midfield, had Leeds's best opportunity of the opening 45 minutes as he raced through on goal early on only to be denied by the swift reactions of Roy Carroll.
At the other end it was Uruguayan international Forlan who came closest to breaking the deadlock for the visitors as he was fed through the middle by Nicky Butt's well aimed pass.
Paul Robinson, in the Leeds goal was equal to his low shot, however, and ensured the teams went in level at the break.
The second half started at a more testing pace and Junior's close-range header, rising unmarked, to meet Ian Harte's 49th-minute cross, gave Leeds the lead.
Ridiculed by so many for his defensive displays since arriving at the club, his goals last night will at least have repaid some of the faith shown in him by manager Peter Reid.
Even with so many of their star names missing Manchester United were never going to sit back and accept defeat against their cross-Pennines rivals though and through the midfield endeavour of Butt they launched a fightback.
Bellion thought he had equalised just before the hour when he turned in Forlan's wayward effort only to see referee Paul Durkin rule it offside, and Forlan himself went close again when he struck a fierce effort from the left wing only to see Robinson make a fine save.
The Leeds goalkeeper was called into action again in the 75th minute when Bellion struck a low drive from the edge of the area, but while the England goalkeeper saved that effort he was helpless to prevent the young Frenchman from equalising three minutes later.
Djemba-Djemba played a cute ball in behind the Leeds defence and Bellion raced through untouched to tuck a low strike through Robinson's legs.
Forlan thought he had won it and Junior then believed he had done enough to take the game to spot kicks, but Djemba-Djemba had other ideas.
Leeds United: Robinson; Kelly, Camara, Junior, Harte; Milner, Johnson, Olembe (Lennon 59), Sakho (Chapuis 79); Smith, Bridges (Domi 71).
Manchester United: Carroll; P Neville, G Neville, O'Shea, Fortune; Fletcher, Djemba-Djemba, Butt, Richardson (Eagles 65); Forlan, Bellion.
Referee: P Durkin (Dorset).