The Premier League clubs played out an eventful game in Sunday's Wembley final, with the United forward proving to be the match winnerZlatan Ibrahimovic scored with three minutes remaining to give Manchester United a thrilling 3-2 victory over Southampton in the EFL Cup final.
A dramatic contest at Wembley was settled when Ibrahimovic headed in Ander Herrera's cross just as the match appeared destined to move into extra-time.
A controversial and thrilling match saw Southampton have Manolo Gabbiadini's strike wrongly ruled out for offside before Ibrahimovic struck with an impressive free-kick at the other end.
Jesse Lingard got the second, finding the bottom-right corner after a neat team move to net on his third consecutive Wembley appearance for United, before Gabbiadini got a goal that did count in first-half stoppage time.
Gabbiadini made it five goals in three Saints matches with a magnificent finish early in the second half, but Ibrahimovic had the last word with his 26th goal of the season.
United have now won the tournament on five occasions, a record bettered only by Liverpool.
Mourinho claims the first major trophy of his United reign and his fourth overall victory in the competition, tying the record jointly held by Brian Clough and Alex Ferguson.
Southampton's wait for a first EFL Cup goes on as their FA Cup success in 1976 – which came against United – remains their only major trophy.
Claude Puel has now lost both of his management appearances in major domestic cup finals, having been beaten as Monaco boss in the 2001 Coupe de la Ligue final.