When Danny Loader broke in on goal and rounded Romero, the 18-year-old's nerves appeared to get the better of him and the United goalkeeper was able to tackle.
The game will pitch the Norwegian against the man who remains favourite to become the next United boss on a full time basis - Mauricio Pochettino. Marcus Rashford is certainly playing with confidence running through his veins and Romelu Lukaku is also back in the goals, but there is one star who is growing into his role at the club in eye catching fashion.
Solskjaer played a virtual reserve team, sticking to his promise to give all his squad a chance to impress, and Mata scored the opening goal in the 22nd minute.
United will spend four days in Dubai before travelling back to Manchester on Thursday.
Instead, Man United were a bit too relaxed for this occasion.
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Congressional leaders have been trying to tamp down talk of impeachment by rank and file members, though Judiciary Chairman Rep. Republicans, meanwhile, sought to turn the tables on Democrats, claiming they aren't interested in getting things done.
The pair, who came on to great effect at Newcastle on Wednesday night, have struggled for form and fitness this season but the hope is they can turn their fortunes around during Solskjaer tenure. Ashley Young and Diogo Dalot will occupy the full-back positions.
That winning sequence continued against second-tier strugglers Reading, with the third round marking the entry into the FA Cup, the world's oldest senior knockout football competition, of England's top-flight clubs. But we made nine changes, and they hadn't played together as a unit so I made it hard for the boys.
Mata dispatched a cool penalty - his first FA Cup goal since the victorious final of May 2016 - after referee Stuart Atwell penalised Omar Richards for a foul on the Spain global after a VAR consultation, with Fred's strike having been disallowed for offside in the same move. After a lengthy delay as VAR was consulted, a penalty was awarded and Mata stepped up to put United 1-0 up.