It is fair to say that the Saints dominated from the off, with Manolo Gabbiadini's disallowed goal before Ibrahimović opened the scoring in the 19th minute. Going behind didn't stop Claude Puel side's with chances for James Ward-Prowse and Dusan Tadic before Jesse Lingard doubled United's lead, but Gabbiadini managed to claw one back to end a thrilling half.
The Italian secured an excellent comeback three minutes after the restart, half chances from Cedric Soares and Oriol Romeu followed but couldn't add to the scoreline. It looked like that it would be heading to extra-time, but a header three minutes from time secured the club's third trophy in ten months.
Against the run of play
It was yet another trip to Wembley Stadium for the Red Devils, and it was set to be a big occasion but looked to be in for a tough afternoon against a scintillating Southampton side.
The red and white side of the national stadium were in mass celebrations 11 minutes in when Gabbiadini managed to turn home Cedric's low ball into the box which was wrongfully ruled offside.
Totally against the run of play in the early proceedings, United managed to take the lead in some style. Ibrahimović punished a poor tackle from Romeu as he hit a free-kick over the wall and into the corner beyond Fraser Forster.
Taking the game to them
Falling behind didn't seem to faze Puel's side as they continued to bombard United's defence and will be baffled how they didn't claw their way back into it. Gabbiadini had been involved heavily throughout the opening proceedings and was at it again, as he held the ball up on the edge of the area before laying it off to Ward-Prowse. It was an excellent effort from the defender, stinging the palms of David De Gea.
Tadic had another great opportunity just after the half-hour mark as he ghosted his way past Paul Pogba to get onto Nathan Redmond's through ball. He managed to get his shot away and once again De Gea was there to save with his feet.
Striking once again
United had hardly been in the contest, but they certainly couldn't be criticised for not taking their chances as they somehow managed to find themselves two ahead with seven minutes to play.
It was liquid football from Jose Mourinho's side, Juan Mata, Anthony Martial and Marcos Rojo all combining brilliantly. The ball came to the feet of Lingard, and the youngster kept up his form under the Wembley arch as he easily rolled it into the far corner.
Turning the game on its head
It was expected that the Saints would have rolled over after Lingard's effort, but Gabbiadini didn't read the script as he turned the game on it's head either side of half-time.
In added time of the first period the Italian managed to pull one back, and it proved easy as he surged towards the near post to get on the end of Ward-Prowse's cross to put it through De Gea's legs.
They came flying out of the traps at the beginning of the second period, and their excellent turnaround was complete three minutes after the restart. It was poor from a defensive stand point for United, as the ball fell to Gabbiadini and he was allowed to turn and volley past De Gea.
Southampton deserve to lead
The momentum was definitely with the South Coast side, and they had two excellent opportunities to grab what would have been an excellent victory.
It was simple enough for Steven Davis as he flicked the ball over to Cedric, playing a dangerous ball across the face of goal and Antonio Valencia did well to turn it behind.
From the subsequent corner Southampton were a lick of paint away from the lead, as Romeu rose highest to the corner into the area and his effort had De Gea stranded but it clashed back off the post.
Stepping up once again
United managed to make it through the onslaught, and just when it looked like it was heading to extra-time Ibrahimovic stepped up once again to secure the victory.
It was simple enough for the Swede as he headed home his 26th goal of the season from Ander Herrera's cross, Many will say that Forster should have done better but it is difficult to look past the Ibrahimovic factor.