On his Premier League debut, the 19-year-old turned from Saint to sinner with a red card inside 74 seconds after a late, two-footed out of control lunge on Scott McTominay. From then on, the result was never really in any doubt as Aaron Wan - Bissaka, Marcus Rashford, Edinson Cavani, a Jan Bednarek own goal, Scott McTominay, a Bruno Fernandes penalty, a brace from half time sub Anthony Martial and another for Dan James saw United equal their own 26-year old record. In March 1995, Sir Alex Ferguson's side beat hapless Ipswich by the same margin at Old Trafford. This result meant that only one other manager has ever done so at home, some chap by the name of Ole Gunnar Solskjaer.
For beleaguered Saints and their manager Ralph Hassenhuttl, it's surely the first instance of a team, under the same manager, losing 9-0 twice in as many seasons after last term's infamous drubbing by Leicester.
Solskjaer made one change from the weekend draw at Arsenal as Mason Greenwood replaced Paul Pogba wide on the right.
Southampton often prove tenacious and energetic opponents, but Jankewitz took that mantra to the extreme with a horrific challenge on McTominay on halfway, leaving referee Mike Dean with little choice but to brandish the red card. The challenge seemed to get worse with every replay, with a red gash on McTominay's thigh showing the extent of the damage.
With the injury hit visitors further depleted by their numerical disadvantage, Southampton's task looked even harder and they had no answer as the rampant Reds soon made them pay. Fred flashed a shot wide from distance and Alex McCarthy saved well from Rashford before Wan - Bissaka opened the scoring with his second of the season after his fellow full-back Luke Shaw had picked him out with a stunning cross to open the floodgates.
Rashford then found the net seven minutes further on as he swept in from close range having linked up with young forward Mason Greenwood for a goal made the United Academy. Saints briefly threatened a response in familiar fashion when David De Gea saved well from a trademark free-kick from Southampton's dead ball specialist James Ward - Prowse.
Bednarek turned home a Rashford ball for 3-0 with Fred lurking and Edinson Cavani then kept up the goal glut with a headed fourth shortly before half-time. The Uruguayan went down under a challenge from Jack Stephens and a penalty was awarded, only for VAR to intervene and downgrade the offence to a free-kick having adjudged the foul to have taken place on the edge of the box.
Solskjaer opted for two half-time subs as Donny van de Beek and Martial replaced the again-impressive Shaw and Cavani, with Fred dropping to left-back.
Southampton looked to have stemmed the flow and restricted the damage but the Reds went close again through Rashford - denied by McCarthy - and Martial, whom fired wide after a good ball from McTominay. At the other end, Che Adams thought he had netted a consolation, only for VAR to spot an offside infringement and the goal was chalked off.
The much-malinged Frenchman got himself on the ever lengthening score sheet on 69 minutes when Bruno Fernandes picked him out and Martial spun his marker to hammer a brilliant finish high into the roof of the net
McTominay drilled in a superb strike for 6-0 two minutes later as the Reds approached remarkable, record sniffing territory.
Fernandes was hunting a goal and got his wish three minutes from time as the Saints implosion continued. Martial was scythed down by Bednarek as referee Dean, this time, gave a spot-kick with the Southampton centre-back - somewhat harshly - sent off for his troubles.
The Reds emulated the seven-goal margin of victory at Nottingham Forest in 1999, a match feted for Ole's four-goal salvo as a sub, as Fernandes thumped home the resultant penalty.
But we would go on to surpass even that, hitting eight for the first time since that famous win over Arsenal in 2011, in an amazing ending to a historic night. Having ended his eight-game goal drought, Martial hooked home from close range after Greenwood had flicked on another cross from the buccaneering Wan - Bissaka.
With the utterly outclassed nine men of Southampton praying for the whistle to put them out of their misery, there was still time for a ninth as substitute James knocked in from close range after Fernandes had cut the ball back.
Overall team performance: 10/10
United Faithful Man of the Match: Aaron Wan - Bissaka. Excellent in both attack and defence and capped a scintillating showing with a rare goal. Magnificent.