Zlatan Ibrahimovic's late header secured Manchester United the first major trophy of the Jose Mourinho era, breaking Southampton hearts close to the end of a thrilling EFL Cup final.
Wembley witnessed a superb encounter as United faced a Southampton side looking to win the second major trophy in their history, the first having come when these two sides met in the FA Cup final 41 years ago.
Manolo Gabbiadini's brace had Southampton dreaming as strikes by Ibrahimovic and Jesse Lingard were cancelled out -- but Ibrahimovic headed home three minutes time to clinch a hard-fought 3-2 win.
Europa League and FA Cup glory remain further possibilities for United this term, but Mourinho will know his players need to up their game.
After Gabbiadini had seen an opening goal inexplicably ruled out, under-performing United showed their ruthless edge as Ibrahimovic fired home a free kick before Lingard scored for a third straight Wembley appearance.
But it appeared a gut punch rather than a decisive blow and Gabbiadini gave Southampton hope with a close-range goal in first-half stoppage time before netting an outstanding leveller soon after the break.
Oriol Romeu crashed a header off the post shortly after avoiding a second yellow card, but it was not to be for Southampton.
Ibrahimovic's 26th goal of the season saw Mourinho become the first United manager to win a major trophy in his debut season, and earned the Portuguese a fourth League Cup triumph -- a joint record with Brian Clough and Sir Alex Ferguson.
But few would have known that United were the side making a record-equalling 49th trip to Wembley as the Saints flew out the blocks.
Dusan Tadic and James Ward-Prowse proved a headache for Mourinho's rattled backline, with Nathan Redmond ending a mazy run with an attempt that deflected wide for a corner.
Southampton should have had a goal in the 11th minute as Gabbiadini turned home Cedric's cross from the right. Inexplicably, though, the assistant raised his flag for offside, despite the Italian being clearly on and Ryan Bertrand off but not interfering with play.
Saints soon had further reason to feel aggrieved. Romeu was booked for a lunge on Ander Herrera, giving Ibrahimovic a chance from 30 yards. It was an opportunity the in-form veteran took with aplomb, firing home a stunning free-kick and wheeling off in celebration.
Saints' wall and goalkeeper Fraser Forster will feel they should have done better with the 19th-minute strike, which Puel's men busily went about cancelling out.
Ward-Prowse and Tadic forced the returning David de Gea into action with efforts from the edge of the box but although United were not attacking with the same regularity, they made their threat count.
Marcos Rojo was allowed through to lay the ball off to Lingard just inside the box, with Southampton's lack of pressure giving the attacking midfielder time to sidefoot past Forster.
But Saints collected themselves. In first-time stoppage time, Ward-Prowse's fine right-wing cross was met by a smart Gabbiadini touch, turning the ball past De Gea.
United's Michael Carrick replaced Juan Mata for a second period in which Southampton started brightly, with Redmond seeing an exquisite volley kept out by De Gea.
Then Steven Davis beat Anthony Martial to a header and Gabbiadini swivelled expertly, firing through a crowd and into the bottom corner in front of the Southampton fans.
It was a moment of utter joy for half of Wembley -- and one Ibrahimovic could soon have rendered worthless, only for Forster to recover from a poor clearance to smother.
Herrera claimed compatriot Romeu should have received a second booking after being clattered, but the appeals were ignored and Romeu soon leaped above Paul Pogba to power a header against the post.
United attempted to make the most of that let-off. A superb challenge from Maya Yoshida prevented Lingard from getting a shot away before the same player blazed over from a glorious 76th-minute chance.
Redmond saw an attempt deflect wide as Saints pushed for a winner, although substitute Marcus Rashford came close at the other end when he forced Forster into a near-post stop.
It was a frantic conclusion and, having blocked a Stephens header from a corner at the other end, Ibrahimovic secured the win.
Unmarked six yards out, he powered home Herrera's cross to secure a memorable win and send United fans wild.