Saints manager Nigel Pearson was the calmest man inside St Mary's after his side completed a dramatic final-day escape from relegation from the Championship.
Stern John cracked a second-half double to add to Marek Saganowski's header as Saints came from behind to beat Sheffield United 3-2 and avoid the drop to League One.
The final whistle sparked bedlam with a mass pitch invasion greeting the news that Leicester had only managed a draw at Stoke, allowing Saints to leapfrog them out of the bottom three.
But afterwards Pearson said: "Relief is the overwhelming feeling at this time.
"At a number of points it looked like we were going to come out on the wrong side, so obviously I'm delighted.
"I didn't know the other scores - some of my staff did but I just wanted to focus on the game. We were up against a side in form and it was never going to be easy."
Having dipped out of the top flight three years ago, Saints were staring down the barrel of third division football for the first time in 48 years when Stephen Quinn nodded the Blades ahead after 23 minutes.
Richard Wright denied the visitors what could have been a killer second when he kept out Matt Kilgallon's point-blank header, and moments later Saganowski scored at the far post to send the teams in level at the break.
John fired Saints ahead at the start of nerve-shredding second half, bringing the ball down in front of goal before dispatching it into the roof of the net.
United substitute Jon Stead looked to have consigned the hosts to the drop once more when he stabbed home.
But John's 20th goal of the season - and comfortably the most important - means St Mary's will once again be hosting Charlton, rather than Cheltenham, next term.
The striker's afternoon ended prematurely when he was sent off for a second yellow card 10 minutes from time, but the 10 men held out.
The win was only Pearson's third since he took over in February, but the man who was in charge of Carlisle when goalkeeper Jimmy Glass scored a last-gasp winner to save them from dropping out of the league can add another great escape to his CV.
Whether Pearson will still be in charge next term remains to be seen, with former chairman Rupert Lowe poised to take over the club again in association with Michael Wilde.
"There are issues which need to be resolved but I'm not in a position to share that information," he added.
"There are decisions to be made at a level at which I'm not involved and there will be, over the next two or three weeks, decisions to be made at every level."
When asked if he thought he would still be in charge next season, Pearson added: "I certainly hope so."
Saints will be meeting Sheffield United again next term, after their lingering hopes of a play-off place were extinguished.
"For a small period at 1-0 we were in the play-offs - and I wish the referee had blown up then," said Kevin Blackwell, who agreed a a permanent contract as Blades manager on Saturday.
"It was important that we gave it a go and we did.
"Over 46 games you merit where you should be but credit to Southampton. It was an incredible atmosphere and pure theatre."
For the best reports, reaction and pictures from St Mary's, don't miss tomorrow's Daily Echo.
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