Manchester
United led 2-0 inside 10 minutes thanks to Lacey's first senior goal and
Mount's quick follow-up, but Brighton fought back with goals from Kostoulas,
Groß, and substitute De Cuyper to win 3-2.
It was the first home loss after leading by two goals in over 50 years, extending Brighton's strong record with five wins in their last six Old Trafford visits.
Michael Carrick took full responsibility, calling the second-half collapse unacceptable, while fans vented their frustration in the stands and online.