The in-form Graziano Pelle scored twice while Dusan Tadic, another of Ronald Koeman’s impressive summer signings, scored one and set up four more in a remarkable performance by the home side, who bounced back from a defeat at Tottenham Hostpur in their last outing before the international break.
Southampton have now won seven of their last eight games in all competitions, while Sunderland remain with just one Premier League win this season after a miserable performance which included two own goals by Santiago Vergini and Liam Bridcutt.
Argentine defender Vergini set the ball rolling with an extraordinary own goal in the 12th minute, inexplicably volleying past his own goalkeeper from 18 yards.
However, nobody could have predicted at that point that Sunderland, having conceded just seven times in their opening eight games this season, would go on to collapse so dramatically.
They fell 2-0 down in the 18th minute when a low ball across goal by Steven Davis was turned into the net by Italy striker Pelle for the 100th club goal of his career.
The Saints were well and truly on top and Jack Cork bundled in a Tadic ball from the left in the 37th minute to make it 3-0 to the hosts at the interval.
Things only got worse for Sunderland in the second half, with Bridcutt helping the ball into his own net in the 63rd minute after Mannone had spilled Pelle’s initial effort.
And Pelle, the Premier League’s player of the month for September who scored Italy’s winner in a Euro 2016 qualifying play-off in Malta in midweek, swept home a Tadic through ball for his second of the game to make it 5-0 on 69 minutes.
Tadic then got his name on the scoresheet with 12 minutes remaining, curling into an empty net after Mannone had somehow managed to give the ball straight to the Serb.
The rampant Tadic set up substitute Victor Wanyama to slam home the seventh a minute later and Tadic then teed up another substitute, Sadio Mane, to make it 8-0 four minutes from time.
Southampton fell one goal short of equalling the Premier League record winning margin, set by Manchester United in a 9-0 mauling of Ipswich Town in 1995, but that will come as no consolation to a sorry Sunderland.