Three days after kicking off League One with an impressive triumph at AFC Wimbledon, Paul Warne’s much-changed side found things harder in the newly-rebranded Leasing.com Trophy.
Man United had never before fielded an Under-21s side in the competition and started Group H with a bang thanks to fine Ethan Laird and Largie Ramazani goals in a 2-0 win at the New York Stadium.
This was always going to be a tough ask for Rotherham given the quality they were facing, with Angel Gomes, James Garner and Tahith Chong dropping down to the development side having featured regularly for Ole Gunnar Solskjaer’s first-team in pre-season.
Warne’s heavily-rotated side did, though, hold their own in the first half and would have gone ahead after the break through Carlton Morris was it not for an exceptional save by Matej Kovar.
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But the Millers’ resistance would finally break as a thumping Laird strike and smart Ramazani finish in quick succession saw the opener go the way of the visitors.
Doncaster, whose manager Darren Moore was in attendance, and Lincoln await in the remaining EFL Trophy matches.
The visitors, perhaps unsurprisingly, started on the front foot and Chong - who was on the pitch during March’s astonishing Champions League win at Paris St Germain - forced Lewis Price into action inside eight minutes.
Under-17 World Cup winner Gomes twice went close with free-kicks in the first half, but the Millers looked capable of landing a blow.
Freddie Ladapo proved a handful and denied by goalkeeper Kovar during the opening period, while his cutback to summer signing Jamie Lindsay deserved better.
Neil Wood’s side kicked on after the break as Chong, Di’Shon Bernard and Dylan Levitt tried their luck before Rotherham went close, with Morris’ sweet strike bound for the net until Kovar superbly tipped around the post in the 58th minute.
Sub Michael Smith was unable to seriously test the goalkeeper from ex-Red Matthew Olosunde’s cross when Warne’s men next threatened and soon Man United’s quality told.
Price did well to push over Ramazani’s attempt but the experienced goalkeeper could do nothing to prevent Laird’s strike moments later, with his thumping 69th-minute opener finding the bottom corner.
Hopes of getting anything out of the match would be extinguished four minutes later.
Gomes won possession deep in his own half and Garner fired a stunning ball up to Ramazani, who cut in impressively and sent a smart left-footed shot past Price.
The Millers struggled to recover from that gut punch, with Levitt rattling the post late on and Chong being denied for Man United.
Rotherham: Price, Hinds, Wood, Cooper, Olosunde, Lindsay (MacDonald, 68), Barlaser (Crooks, 46), Wiles, Ladapo (Smith, 54), Morris, Proctor. Unused subs: Bilboe, Robertson, Ihiekwe
Manchester United Under-21s: Kovar, Laird, Bernard, O’Connor, Williams, Garner, Levitt, Ramazani, Gomes, Chong, Mellor. Unused subs: Fojticek, Ercolani, Tanner, Galbraith, McGhee, Puigmal, Traore
Attendance: 3,105 (435 away)