Southampton, who played with 10 men for pretty much the whole game after Alexandre Janktewitz was sent off after just 79 seconds before having Jan Bednarek sent off late on, were blown away by the relentless Red Devils.
Two goals from Anthony Martial, and one each from Scott Mctominay, Marcus Rashford, Aaron Wan-Bissaka, Bruno Fernandes, Edinson Cavani and Dan James, as well as an own goal from Jan Bednarek gave United their joint-biggest win in Premier League history.
Nightmare Start for Saints
Southampton’s hopes of a first win at Old Trafford since 2016 were dashed almost instantly when 19-year-old midfielder Alexandre Janktewitz, making his first start for the Saints, was sent off for a horrific challenge on Scott Mctominay within the first two minutes.
From then onwards, it was all United as four quick-fire first half goals put the game to bed.
Luke Shaw grabbed two assists from two brilliant crosses to continue his recent good form, whilst Aaron Wan-Bissaka scored only his second ever Premier League goal.
It was Wan-Bissaka who opened the scoring after just 18 minutes after being picked out at the back post by fellow full-back Shaw.
Marcus Rashford bagged the second of the night, and his 15th of the season, following a good cross from Bruno Fernandes before a Jan Bednarek own goal and a fantastic header by Edinson Cavani gave United a 4-0 lead going into half-time.
United made two substitutions at half-time, bringing on Donny Van De Beek and Anthony Martial and it was Martial who continued the rout in the second half, scoring the fifth goal before Scott Mctominay fired a thunderbolt past Saints keeper Alex McCarthy for goal number six.
Bad to worse for Southampton
Having had a penalty overturned in the first-half, there was no doubt about this one as Jan Bednarek cynically brought down Martial in the box just as he was about to fire a shot at goal.
Having consulted VAR, referee Mike Dean decided to send Bednarek off for the foul, leaving Southampton with just nine players on the pitch.
Bruno Fernandes scored the resulting penalty, his seventh goal from the spot this season, to put United 7-0 up, a margin of victory they hadn’t seen since Ole-Gunnar Solskjaer scored four in an 8-1 victory against Nottingham Forest in 1998.
It was to get even better for United, however, as Anthony Martial scored his second of the game, which will surely boost his confidence after a pretty lean spell in terms of goals, before Dan James completed the rout to match the same score line that Southampton lost to Leicester City by last season.
The Saints become the first team in Premier League history to have been beaten by such a high score line both at home and away.
United, on the other hand, matched the same score line as they beat Ipswich Town by in 1995 and massively improved their goal difference which could be so crucial in such a tight title race.