In-form Saints forward Graziano Pelle scored either side of half time, while one each from Jack Cork, Dusan Tadic, Victor Wanyama and Sadio Mane compounded the misery after Liam Bridcutt had too put into his own net.
The visitors were out of the contest by the break, allowing the Saints to put on a real show and delight their fans.
Here, Sports Mole attempts to analyse an extremely one-sided encounter.
On target: 12
On target: 1
Was the result fair?
Any game in which one of the teams score eight times must surely mean that the result was a fair one. This was a total masterclass from the hosts, who never looked back once Vergini's bizarre own goal gave them a 12th-minute lead. Sunderland struggled to cope with the pace of the Saints, who ran them ragged even before a five-goal frenzy in the second half. After the interval, it descended into a bit of a farce with Southampton attacking at will and Sunderland looking more and more lost as the game went on.
With Dusan Tadic pulling the strings and Graziano Pelle finishing the chances, Southampton really do look capable of challenging the European spots this season. They were magnificent today - in a way that very few of the 'big' teams have looked so far this term. Every time that they attacked, they looked capable of scoring a goal, and more often than not today, they did. It is difficult to summarise just how dominant the hosts were this afternoon. Astonishing stuff from Koeman's exciting team.
The worst display that will be seen in the Premier League all season, from a Sunderland side who looked to have given up by the time the fourth goal went in. It was bitterly disappointing for Poyet to see his team collapse in the fashion that they did, and they only have themselves to blame for that. From the own goals of Vergini and Bridcutt to the awful errors of Vito Mannone in goal, this was a shocking day at the office for a Black Cats side that had only lost once previously in the league all season.
Sports Mole's man of the match
As may have been suspected a number of Southampton players made extremely strong cases for this award today. However, the Serbian midfielder at the heart of it all must take the main plaudits. As well as setting up four of side's goals, he added one himself after a poor clearance from Mannone. Some of his footwork was majestic, especially in tight areas, and his eye for a pass or a cross cannot be questioned. Simply sublime.
On reflection of the goals, at least four were probably avoidable from a Sunderland point of view. In truth though, Vergini's volleyed effort into his own net was the most shocking of the lot. With Shane Long looking to get on the end of a bouncing ball, Vergini cut in front to intercept, but, instead of firing into the stands to clear, he connected with the ball impeccably, arrowing the ball past Mannone and into the bottom corner. It will take quite a lot to see a more unbelievable own goal scored this season.
Poyet may have complaints that his side should have had a penalty at 2-0, but the truth is that Sunderland were so much the poorer team that it would not have changed anything. Andre Marriner did not have a decision to make after half time, with Southampton running riot and the Black Cats unable to get anywhere near them.
Southampton: Stoke City are the next team to make the trip to St Mary's when they visit next Saturday.
Sunderland: Poyet will look for his team to bounce back at home to Arsenal in a week's time.