There could have been no more fitting way to decide a match that was a long way from being technically perfect but for which the term eventful falls well short. Butt had already made a huge contribution with his tireless industry when he took a pass from Phil Neville on the edge of the penalty area with 13 minutes remaining, turned and shot past Leeds' substitute goalkeeper, Paul Robinson, in stunning fashion.
That sent Leeds back across the Pennines empty-handed, but they emerged with great credit from this game. From time to time, their vocal wedge of supporters at Old Trafford sang "Batty's coming home"; there was a good deal of that returning prodigal's tigerish determination in this display, unrewarded as it ultimately was.
A Leeds defence already lacking several key members was under heavy pressure even before the loss of two more in the first half. Martin Hiden was stretchered off with a knee injury and almost immediately Nigel Martyn hurt his back getting his fingertips to Butt's goalbound header to divert it on to the bar.
Concern over those events was lifted somewhat when, completely against the run of play, the visitors took the lead. Jimmy Floyd Hasselbaink took a pass from Harry Kewell to the left of the goal and, with Phil Neville failing to close him down, fired in a low right-footer that cannoned in off the foot of Peter Schmeichel's post.
Martyn tried to soldier on and Leeds even had a chance to double their lead when Kewell lobbed wide of an exposed target. With half-time approaching, however, Roy Keane backtracked to keep an attack moving, Dwight Yorke ran at the defence and released Ole Gunnar Solskjaer for the Norwegian to beat the struggling Martyn from an acute angle.
It was no surprise that the England goalkeeper failed to reappear for the second half and within 20 seconds of replacing him Robinson, Leeds' third choice in the position, was picking the ball out of the net.
Not that Martyn or anyone else could have done a great deal about it, such was the precision engineering of the goal. Butt's magnificent crossfield pass found Paul Scholes, who twisted Ian Harte in all directions before getting in a low cross from the byline. There could be few more daunting sights for a newly-arrived goalkeeper than Keane bearing down on the ball to smash it into the roof of the net from 10 yards out.
That should have been the signal for United to take a more assured control of proceedings, but this was a performance from them that was just like the newly relayed playing surface - loose and uneven.
Within six minutes, a plucky Leeds were level again, Wes Brown's slip allowing Kewell through and a neat chip leaving Schmeichel helpless.
A Manchester side from which David Beckham, Jesper Blomqvist and Denis Irwin were rested after their Barcelona epic called up the reinforcements in a bid to win it. Three recent absentees all got into the action: Ryan Giggs and Teddy Sheringham as tactical changes and Henning Berg out of necessity when Jaap Stam finally succumbed to a virus.
But, after Kewell had missed an opportunity to put Leeds back in front, it was one of the constant factors in the ebb and flow of this game, the excellent Butt, who made the crucial move with his first goal of the season.
"He's had a mixed season and hasn't really had a run at it. He was always a threat and he deserved his goal because he persevered all day," said an admiring Alex Ferguson, who described Leeds' performance as their best at Old Trafford in all his time there. "Leeds deserved a lot of credit. They played very positively and it was a good test for us considering the exertions of the week."
For David O'Leary there was some consolation in defeat. "You need your full 11 when you come here," he said. "But we can get on that coach and know that we gave a good account of ourselves."
Goals: Hasselbaink (29) 0-1; Solskjaer (45) 1-1; Keane (46) 2-1; Kewell (52) 2-2; Butt (77) 3-2.
Manchester United (4-3-3): Schmeichel; Brown, Stam (Berg, 76), G Neville, P Neville; Scholes (Sheringham, 71), Keane, Butt; Yorke, Cole (Giggs, 64), Solskjaer. Substitutes not used: Curtis, van der Gouw (gk).
Leeds United (4-4-2): Martyn (Robinson, h-t); Halle, Hiden (Wetherall, 25), Woodgate, Harte; Haaland, Hopkin, McPhail, Ribeiro (Smith, 84); Hasselbaink, Kewell. Substitutes not used: Wijnhard, Granville.
Referee: G Poll (Hertford).
Bookings: United: P Neville. Leeds: Haaland, Ribeiro.
Man of the match: Butt.
Attendance: 55,172.Reuse content