An epic encounter at Wembley saw Southampton dominate for long periods, then recover from two goals down before Manchester United claimed victory with a Zlatan Ibrahimovic strike three minutes from time.
This encounter was the total opposite of the cagey, defensive affairs that so often characterise finals at Wembley.
But it was Utd who proved the more clinical in front of goal as Zlatan Ibrahimovic opened the scoring by curling a brilliant free kick over the Southampton wall after 19 minutes for his 25th strike of the season
The South coast team could well have let their heads drop but deservedly gave themselves a lifeline on the stroke of half-time; Gabbiadini getting on the end of James Ward-Prowse teasing cross.
Southampton continued where they had left off as the second-half began and levelled within four minutes of the restart. Utd failed to clear a corner and Gabbiadini reacted quickest to restore Saints parity.
Utd were struggling to get into the game but gradually weathered the storm and began to look dangerous themselves. But eventually it was the team from Old Trafford who prevailed as in the space of one minute the fine line between success and failure was cruelly exposed as far as Southampton were concerned.
With four minutes remaining Southampton had two glorious opportunities to take the lead as firstly Ryan Bertrand sent a brilliant ball into the area but Shane Long failed to connect from close range. From the resulting corner Ibrahimovic headed Jack Stephens's effort off the line.
Utd then broke quickly and Ander Herrera sent over a cross which was inch perfect for the Swedish superstar Ibrahimovic to head the winner from six yards.
Breathless stuff and Utd had to endure four minutes of added time before boss Jose Mourinho became the first Manchester United manager to claim a trophy in his first season giving him the silverware for the fourth time after three successes with Chelsea.
But sympathy for the Saints who were the better side in the match, but lapses in concentration and a failure to take their chances cost them dear.
Man Utd: 3 (Ibrahimovic 19, 87, Lingard 38)
Southampton: 2 (Gabbiadini 45, 49)