Mason Mount came on at half-time (Photo by Ash Donelon/Manchester United via Getty Images)
United were a goal down at half-time after Erling Haaland converted a controversial penalty decision.
However, the Red Devils had chances of their own, most notably through Rasmus Hojlund.
But City were completely dominant in the second half, adding goals through Haaland and Phil Foden in a 3-0 win.
United barely laid a glove on City during the second half, with Gary Neville blaming the turning tide on Ten Hag’s ‘reckless’ decision to remove Amrabat for Mount.
Scott McTominay dropped deeper to play alongside Christian Eriksen, but the pair were completely bypassed by City’s midfield.
Mount started on the bench (Photo by Alex Dodd – CameraSport via Getty Images)
But Ten Hag insists he has no regrets in his decision to bring on Mount.
‘We had to create because we were losing the match,’ said Ten Hag.
‘We couldn’t wait and with Mason Mount, we can expect creativity.’
United host Newcastle United at Old Trafford on Wednesday in the Carabao Cup.
Ten Hag is expected to make changes for the tie, with Raphael Varane, Casemiro and Antony likely to come back into the starting XI.
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It was costly.