Manchester United equalled the Premier League record by putting nine goals past nine-man Southampton - the second time Saints have lost 9-0 in as many seasons.
A red card for Saints' Alexandre Jankewitz after only two minutes triggered a complete collapse for the visitors, who were on the end of the same scoreline against Leicester City in October 2019.
It is only the third time a team has lost 9-0 in the Premier League, with United also beating Ipswich Town by that margin in 1995.
Aaron Wan-Bissaka opened the scoring with his first goal at Old Trafford.