Rather than getting his side back into the contest, Luke Ayling's 49th-minute equaliser prompted an avalanche of Manchester United goals - four in 16 head-spinning minutes.
For anyone to cope with hat-trick-scorer Bruno Fernandes and Paul Pogba, who made four goals, in this mood would have been difficult but it was a job for a professional, not an amateur.
Of all the players Leeds struggle most without Kalvin Phillips is probably top of the list.
Marcelo Bielsa chose not to push Phillips straight back into the heat of battle and instead called on centre-back Robin Koch - not new to the position, but no specialist either. Pogba was playing out of position too on the left wing, but it worked in his favour.
With Phillips having played the most minutes for finalists England at Euro 2020, Bielsa erred on the side of keeping him on the bench.
Koch has played as a holding midfielder for Germany and did so again in pre-season but Fernandes and Pogba caused him all sorts of problems. They just would not stand still.
Often when they swapped Koch would stick with the more central player but it was tough mentally as well as physically and allowed the Portuguese to get on top.
The first real warning came in the sixth minute when Fernandes dropped deep and took Koch out of the game by backheeling to release Scott McTominay. Mason Grenwood's shot was mercifully weak.
The Red Devils were confident, particularly Koch and Pascal Struijk, who was played into trouble in the 11th minute, only to be helped out by Illan Meslier rushing off his line to deny Greenwood.
Pogba looked certain to score when Greenwood beat Struijk minutes later and released him, but rippled the side netting.
McTominay, Pogba and Fernandes were all involved in the opening goal, a Meslier goalkick relayed between them and whilst the goalkeeper was quick off his line again and spread him well, Fernandes's shot went in off the inside of his right calf.
Leeds had to that point produced odd flashes, often when they got central midfielders into the right corner. McTominay had to cut out Mateusz Klich's ball from there, and Victor Lindelof Rodrigo's. Jack Harrison produced a good effort before the corner was cleared and Klich forced a much more difficult save a couple of minutes later.
The Red Devils were having more of the ball but Leeds's counter-punches were dangerous. Harrison won a free-kick with brilliant footwork but Rodrigo headed it wide.
Once they went behind, though, Leeds tottered for the rest of the first half and the breakaways stopped.
Bielsa made a change at half-time but it was not to bring Koch off, just introduce Junior Firpo so that Stuart Dallas could move alongisde him.
Dallas's square ball set up Ayling's equaliser, though it was such a fantastic finish, talking about assists seemed churlish.
Brilliant as it was, it turned out to be the worst thing he could have done, though, provoking two goals in as many minutes.
Pogba's ball to Greenwood was perfectly weighted but it looked like Struijk had perhaps forced him wide enough for safety. The Bradfordian, though, is an expert finish, even from tight angles. Meslier had no chance.
Pogba's pass to Fernandes was almost as good and when Ayling thought he had cleared off the line, the referee's watch told him otherwise. The goal would never have stood without goalline technology.
It broke Leeds.
Lindelof's pass to send Fernandes was just a straight one but with Ayling playing him on, again by a very narrow margin, the Portuguese thumped home his hat-trick.
After 68 minutes the tin lid was put on it when Pogba popped up in the left wing position he was actually supposed to be in and picked out the goal-shy Fred for a tap-in.
When the game had become a procession, Koch had a shot at redemption, his quick thinking allowing him to step in and play a pass to substitute Tyler Roberts, who teed up Raphinha. He shot wide.
It was one defeat. Last season's at Old Trafford actually seemed to do the Whites some good but it was yet another day this sumer where Phillips's reputation was enhanced.
Manchester United: de Gea; Wan-Bissaka, Lindelof, Maguire, Shaw; McTominay (Matic 69), Fred; James (Sancho 75), Fernandes, Pogba (Martial 75); Greenwood
Unused substitutes: Mata, Pereira, Dalot, Heaton, Williams, van de Beek.
Leeds United: Meslier; Ayling, Struijk, Cooper, Dallas; Koch; Raphinha, Klich, Rodrigo (Firpo 46), Harrison (Costa 69); Bamford.
Unused substitutes: Forshaw, Roberts, Klaesson, Phillips, Summerville, Greenwood, Shackleton.
Referee: P Tierney (Wigan).