Match ends, Southampton 0, Leicester City 9.
Leicester City equalled the 24-year-old record for the biggest ever Premier League victory as 10-man Southampton were dismantled at a rainswept St Mary's.
The victory sees Brendan Rodgers' side climb into second place, leapfrogging Manchester City and moving five points behind leaders Liverpool.
The result, which matches Manchester United's 9-0 win against Ipswich in 1995, was only confirmed in stoppage time thanks to Jamie Vardy's penalty.
Both Vardy and Ayoze Perez scored hat-tricks, with the visitors aided by Ryan Bertrand's red card for a reckless challenge on Perez in the build-up to Ben Chilwell's opener.
That opened the floodgates for Leicester, who turned on the style just two days before the first anniversary of the helicopter crash that killed the club's former chairman Vichai Srivaddhanaprabha and four other people.
Youri Tielemans also scored his third goal of the campaign and James Maddison added a superb free-kick on a miserable evening for Southampton, who drop into the bottom three.
On a landmark night, Leicester also:
- recorded the biggest ever victory by an away side in an English top-flight league match in the 131-year history of the Football League
- inflicted Southampton's biggest ever defeat as an English league side in all competitions in their history
- became only the second team in Premier League history to establish a five-goal lead in the first half of an away game in the competition, after Manchester City against Burnley in April 2010 (also 5-0)
- became only the second side in Premier League history to have two players score a hat-trick in the same game (Perez and Vardy), after Arsenal in May 2003 - also against Southampton (Pennant and Pires)
Lethal Leicester serve notice of intent
Leicester may have played a game more than Liverpool but this emphatic result means that they have now scored more goals than the league leaders and are just four behind Manchester City.
And the omens look good for Rodgers' side who have now collected one point more from the opening 10 games of the current season than at the same stage of their title-winning campaign in 2015-16.
With trips to Crystal Palace and Brighton on the horizon either side of hosting Arsenal, Leicester have every chance to kick on from their strong start, but given the strength and form of Liverpool and Manchester City, a title challenge appears unlikely.
But the manner in which the Foxes ruthlessly cut through the hosts will nevertheless serve as a warning to others, with their three goals inside the opening 19 minutes the fastest they have amassed that scoreline in a Premier League match since 1998.
Also working in Leicester's favour is the attacking menace still being provided by Vardy.
While the forward is approaching his 33rd birthday, there are few signs, if any, that his physical capabilities are waning and he looked as sprightly as ever as he recorded his first hat-trick for almost three years.
His first showed nimbleness and awareness as he cut inside Saints defender Maya Yoshida to drill a close-range effort into the bottom corner, while his second showcased smart movement as he headed past Angus Gunn from close range. His trademark blistering pace then took him clear of the Southampton defence to win and convert a late penalty.
His exploits were also complemented by Perez, who opened his account for the season after finding the bottom-right corner following a neat one-two with Tielemans.
The Spaniard then superbly swept home Chilwell's pinpoint cross for his second before finding the bottom corner with a left-footed shot to complete his treble.
- Football Daily podcast: It's raining goals... for Leicester
- Reaction to Leicester's record-equalling victory at Southampton
What does this mean for sorry Southampton?
At the start of the evening Southampton's focus was purely on ending a barren run of seven games without a home win dating back to April.
But by half-time manager Ralph Hasenhuttl had changed tack considerably, by simply trying to avoid any further embarrassment.
The Austrian, who at times appeared exasperated and spent much of the interval sitting in his technical area, introduced Kevin Danso and Jack Stephens to replace Jannik Vestergaard and Danny Ings, but it was too little to late.
With the crowd visibly thinning in the second period, Hasenhuttl must now hope the scale of this defeat has not eroded the confidence of his players too much.
While the Saints are a couple of points better off than at the same time last term, they appear in danger of being dragged into another relegation fight.
And their road to redemption is unlikely to be an easy one with their next two fixtures away at Manchester City in both the Carabao Cup and Premier League.
Man of the Match - Ayoze Perez
'We were ruthless' - what they said
Leicester manager Brendan Rodgers, speaking to BBC Match of the Day:
"I'm very pleased to see our work rate, we scored some great goals and we were very hungry tonight. It was horrible weather but our focus was outstanding. I'm very pleased how we defended, and we were ruthless. I'm very proud to stand and be the manager of that team.
"We wanted to get the ball back quickly and attack again. A mark of the good sides is you don't let up. We wanted to show we're a good side and we certainly did that in the second half.
"We were ruthlessly simple in our game. When you're so many goals up you can easily slow but we kept focused. We want to be a top team and to be a top team you must be clinical.
"It was a very good team performance and we're pleased to keep a clean sheet. It's good for our goals for but the clean sheet is equally important."
Southampton manager Ralph Hasenhuttl, speaking to BBC Match of the Day:
"That was one of the tough ones tonight. The performance was a disaster today and I have to apologies and take 100% responsibility - I've never seen a team act like this, there was no fight for anything.
"It was horrible to watch and everyone who stayed to watch is really a fan of this football club. Leicester were in every part of the game better than us I'm a proud man but the way we play today is not the way I want to see my team play. We must get our heads up and that is my job in the next few days.
"I said we must play to the last minute but I can understand why the fans that left. We all must to do everything to pull this back. I haven't looked at the [Ryan Bertrand] red card but it doesn't make any difference in this moment."
On what was said after the game: "There is nothing I want to speak of here in front of the camera - we keep that for in the dressing room."
Southampton travel to Manchester City in the Carabao Cup on Tuesday (19:45 GMT) before returning to the Etihad in the Premier League on Saturday, 2 November (15:00 GMT).
Leicester travel to Burton in the EFL Cup also on Tuesday (19:45 GMT) before going to Crystal Palace in the Premier League on Sunday, 3 November (14:00 GMT).
- 4VestergaardSubstituted forDansoat 45'minutes
- 43ValerySubstituted forS Armstrongat 70'minutes
- 21BertrandBooked at 12mins
- 9IngsSubstituted forStephensat 45'minutes
- 17S Armstrong
- 21Ricardo Pereira
- 17PérezSubstituted forGrayat 74'minutes
- 15BarnesSubstituted forAlbrightonat 72'minutes
- Andre Marriner
- Shots on Target
Second Half ends, Southampton 0, Leicester City 9.
Goal! Southampton 0, Leicester City 9. Jamie Vardy (Leicester City) converts the penalty with a right footed shot to the top right corner.
Penalty Leicester City. Jamie Vardy draws a foul in the penalty area.
Penalty conceded by Jan Bednarek (Southampton) after a foul in the penalty area.
Attempt blocked. Youri Tielemans (Leicester City) right footed shot from the right side of the box is blocked. Assisted by Marc Albrighton with a cross.
Corner, Leicester City. Conceded by James Ward-Prowse.
Attempt saved. Marc Albrighton (Leicester City) right footed shot from outside the box is saved in the bottom left corner. Assisted by Ben Chilwell.
Corner, Leicester City. Conceded by Maya Yoshida.
Offside, Southampton. Jack Stephens tries a through ball, but Nathan Redmond is caught offside.
Foul by Ben Chilwell (Leicester City).
Stuart Armstrong (Southampton) wins a free kick on the right wing.
Goal! Southampton 0, Leicester City 8. James Maddison (Leicester City) from a free kick with a right footed shot to the top left corner.
Jamie Vardy (Leicester City) wins a free kick in the attacking half.
Foul by Jan Bednarek (Southampton).
Attempt missed. Ben Chilwell (Leicester City) left footed shot from outside the box is close, but misses the top right corner. Assisted by Youri Tielemans.
Attempt missed. Nathan Redmond (Southampton) right footed shot from the centre of the box misses to the right. Assisted by Kevin Danso following a corner.
Corner, Southampton. Conceded by Ben Chilwell.
Foul by Wilfred Ndidi (Leicester City).
Nathan Redmond (Southampton) wins a free kick in the attacking half.