It would have been easy to mistake Manchester United’s pre-match insouciance for disinterest.

The supporters’ seats at their east end of the stadium were still largely empty while the popular St Mary’s stadium warm-up act, Kenzie Benali, was encouraging the sea of Southampton red and white to make some sound. “I can feel the buzz. You guys keep what you’re doing,” she told them. Southampton were the wide-eyed idealists.

There was a tell-tale sign just before kick-off, though, of the supreme significance of the occasion for the Manchester team and their manager. The players had just completed the national anthem when he walked down his line of men and shook them by the hand, one-by-one. This used to be the job reserved for royalty but the king of the cup terrain was doing what he does: extracting every last ounce of psychological capital.

The point seemed to have been pressed on the team a little too forcibly, judging by the way that Southampton looked looser, brighter, freer in spirit, even as they fell to what seemed an unsalvageable deficit in the first 40 minutes. Southampton were the ones with all the width, exploiting it to trouble United from both flanks which was certainly something, given that this is a team who had not conceded more than one goal in a football match since October. Despite the game’s late twist, Nathan Redmond and Ryan Bertrand wrote their names cross Wembley.

There was an ominous sense that history might be repeating itself when Manolo Gabbiadini was unjustly denied the opening goal. It was in another League Cup final between United and a team unaccustomed to Wembley, Aston Villa, seven years ago, that Nemanja Vidic was not dismissed when he should have been, as the team started poorly, before winning through. It stored up years of Villa indignation.

Gabbiadini's brace gave Southampton hope (Getty)

To have been forced to swallow the Italian’s goal being disallowed and then to concede twice to a side of such mighty proportion would have been too much for most teams, though not Southampton. Their recovery restored us to what we remembered cup finals to be: a game of rich in attacking intent, error and controversy. The first half’s last act of anger came from Redmond, exhorting his side's supporters to bring still more intensity as he left for the dressing room. With his intuitive sense of how a game is going, Mourinho saw the danger ahead. He removing Juan Mata for Michael Carrick at the start of the second half to provide the ballast his side was missing.

Even he could not have bargained for Gabbiadini and his sublime elasticity. Rafael Benitez is one of the managers who could have told him about it. He was quick to give the Italian an opportunity when manager at Napoli because of the danger he posed from close quarters. Behind the unkempt exterior lurks a precision in the box which Benitez always found immaculate. It’s why the decision of Mauricio Sarri, Benitez’s successor, to marginalise Gabbiadini looked so baffling before the player sought refuge in Southampton last month.

This is the first major trophy of Mourinho's United career (Getty)

The Italian’s precise tuck through the legs of David de Gea to bring the side back to parity before the break was one thing. His second goal - Gabbiadini watching the ball loop over Paul Pogba, spinning off Chris Smalling and navigating a finish before Eric Bailly could block - was something entirely different. It was three games, five goals, for the January signing. We seemed to returning to the spirit of 1976 in that moment: ‘Oh when the Saints’ and a sea of red and white striped scarves.

And it was when the blows had been traded, team for team – Oriol Romeu heading against a post and exposing an aerial weakness in Pogba; Jesse Lingard blasting over when a ball sat up for him – that Mourinho’s serial winner stepped up to the mark. “He doesn’t run much,” Claude Puel had said of Zlatan Ibrahimovic before this game - the point being that he does not need to. The Swede’s dance of unmitigated delight when he’d scored his first told the story revealed him to be the agent of Mourinho’s resolve. When Herrera’s pin point cross came in, the No 9 was ready.

Southampton came so close to ending their trophy drought at Wembley (Getty)

Gabbiadini’s title had been wrested from him. ‘Man of the Match: Zlatan Ibrahimovic’ the stadium announcer proclaimed at the end, to a chorus of understandable Southampton boos. The side who did most to create a final for the ages will say it was 3-3 and that their Italian scored a hat-trick.The talk of the disallowed goal will still be consuming them this summer.