United academy graduate Mainoo capped off a phenomenal breakout season, scoring what proved to be the decisive goal as the Red Devils got revenge for last year’s painful defeat to win the competition for a 13th time.
Erik ten Hag’s men entered the half-time break with a two-goal lead after Alejandro Garnacho had earlier capitalised on a defensive mix-up between Stefan Ortega and Josko Gvardiol to open the scoring at Wembley.
Second-half substitute Jeremy Doku pulled a goal back for City in the 87th minute but it was too little, too late and United held firm to end their disappointing campaign on a high, denying Pep Guardiola and co an historic double-double.
The result sealed United a spot in next year’s Europa League and Mainoo was named man of the match for his outstanding display on the biggest stage, with the teenager outshining the likes of Bernardo Silva and Rodri in the middle of the park.
Eyebrows were raised before kick-off as Ten Hag named Sofyan Amrabat in his starting XI. The Morocco midfielder has had a torrid time since joining United on loan from Fiorentina but produced arguably his finest performance in a United shirt.
‘Like a prime [Gennaro] Gattuso today [three clapping emojis],’ legendary ex-United midfielder Scholes wrote on his Instagram stories.
Later on, Scholes – a three-time FA Cup winner with United – responded to fans who had been comparing Mainoo to him in the lead-up to the Wembley showpiece.
‘Read a few comparisons between me and this kid last week… don’t waste your time, he is 10 times the player I was at 19,’ Scholes said.
‘Just love the way he receives the ball, the calmness, the awareness of what’s around him and of course big goals in big games.
‘The boy is special… and he’s a f***ing Red {two heart emojis]… laters.’
With excitement growing over Mainoo’s burgeoning potential, Ten Hag urged supporters to ‘keep calm’ in order for the teenager to develop at his own pace as he spoke with BBC Sport shortly after the final whistle.
Asked whether there was a limit to Mainoo’s potential, Ten Hag replied: ‘He was [great], it was really so enjoyable to watch Kobbie at his age.
‘He’s an example, we wanted to play him but then in pre-season the second game he got a bad injury and took him so long to get back.
‘I think we have to keep it calm. You are very good here in England to push players and managers very high and then to hammer them when they have one or two bad performances.’
Meanwhile, in the BBC Sport studio, Wayne Rooney – United’s all-time goalscorer – picked out Mainoo and Garnacho as the club’s two ‘standout players’ across the campaign.
‘To come into the middle of the pitch and dominate the way Kobbie Mainoo has done for large portions of this season and to perform the way he did against this Manchester City team…,’ Rooney said.
‘Them two have been the standout players for Manchester United this season. For them to be the match-winners is great.
‘I’m really pleased for them.’