Match ends, Southampton 2, Tottenham Hotspur 5.
Son Heung-min said it was "incredible" to score four goals as Tottenham secured their first Premier League win of the season by coming from behind to thrash Southampton.
The South Korea international combined with Harry Kane for all four of his goals as Spurs took control after Danny Ings' fine finish from a tight angle had given Southampton a first-half lead.
"It's incredible to score four goals in the Premier League, it's a big honour," said Son.
"I wouldn't have scored four goals without this guy (Kane). He's amazing. Four assists, he deserved the man of the match today.
"We've been working for five seasons now together, we know what we like."
Son's first came on the stroke of half-time when he raced on to Kane's pass before driving across Alex McCarthy and into the back of the net.
The pair opened up Southampton again as Spurs took the lead soon after the restart, Kane sending Son through one-on-one and the forward making no mistake.
The hosts struggled to deal with Son's superbly timed runs behind the defence and he duly got his third, racing on to Kane's clipped pass before slotting in.
Kane then provided his fourth assist of the day with a brilliant cross for Son, who coolly chipped McCarthy, before Kane got in on the scoring himself when he stabbed in from close range after Erik Lamela's shot had been pushed on to the post.
Ings converted a penalty in stoppage time but it was scant consolation as Southampton slumped to their third consecutive defeat in all competitions.
Alli absent as Son puts on super show
This was a much-needed win for Tottenham after a difficult start to the season in which they were beaten by Everton on the opening day before scraping past Bulgarian side Lokomotiv Plovdiv in Europa League qualifying in midweek.
A significant reason for their defeat to the Toffees was their lack of creativity in midfield - with Dele Alli paying the price in that game for a disappointing display by being taken off at half-time.
Left out of the midweek Europa League tie, Alli was again omitted from the side for the trip to St Mary's, with Jose Mourinho saying his absence was down to having "too many players" in certain positions.
For a long time in this game, Mourinho's bold move looked destined to be the talking point as Tottenham sorely lacked creativity in midfield.
Aside from a couple of disallowed goals for Kane, the visitors barely troubled the Southampton defence and even when they did manage to score right before the half-time whistle it came from Tottenham's only shot and only touch in Southampton's box in the entire first half.
But after the break, Son and Kane took centre stage, taking advantaging of Southampton's high line and slow defence as they demonstrated an understanding that seemed almost telepathic at times.
Kane assisted just two league goals in the entirety of last season but almost every pass he provided in the second half of this game was to set up a Son goal as he became the first player in Premier League history to assist a single team-mate four times in the same match.
With the return of Gareth Bale, Tottenham have the potential for a front three that could rival the very best in the world.
Saints have work to do
A seven game unbeaten run at the end of last season gave Southampton fans plenty of reasons to be optimistic that their side could challenge further up the table this term.
Things have so far not gone to plan. The Saints have been beaten in all three of their games this season, losing to Crystal Palace in their Premier League opener before they were knocked out of the League Cup by Championship side Brentford.
Ings, who scored 22 league goals last season, has been linked with a move to Tottenham in this transfer window and he showed why it is crucial that the Saints keep a hold of him.
His first goal in this game was a superbly taken finish and he was a constant thorn in the Spurs side in a first half Southampton had the better of as he pressured defenders in possession and linked up play in attack.
But Southampton cannot rely on Ings to win games on his own and will need to show better in defence than they did in the second half as time and again they failed to pick up the runs by Son.
"The way we defended was a disaster," conceded Saints boss Ralph Hasenhuttl after the game.
"That is something we will have to speak about because it was stupid. In the end it was a deserved defeat."
We were too good for them - what they said
Southampton boss Ralph Hasenhuttl to BBC Sport: "I think we conceded a stupid goal shortly before half-time. Then we had a big chance for 2-1.
"On the counter-attack it's 1-2. From that our heads are going down and a team with this quality kills you immediately.
"Playing offside all the time doesn't work because of the rule that the linesman has to keep the flag down. It doesn't make sense to do it like this.
"It didn't feel like we were five goals worse than they are."
Spurs manager Jose Mourinho to BBC Sport: "We didn't start bad at all. In the first 10 or 15 minutes we were good. After that we lost control.
"In the centre of our defensive area, we were a bit sloppy. We lost some duels. They got the ball behind us too easy. I was on the bench and thinking I would be happy to get in at 1-0.
"The goal gave us a different position in the game. In the second half, Harry Kane killed the game, the way he connected the game, the way he was dropping, he allowed Son Heung-min into attacking spaces. His performance was amazing.
"In the second half we were too good for them."
Spurs travelling well - the stats
- Since Ralph Hasenhuttl took charge of Southampton in December 2018, his side have squandered more points from winning positions than any other Premier League side (37).
- Tottenham are now unbeaten in four Premier League games away from home (W2 D2), their longest run without defeat on the road since January 2019 (four straight wins under Mauricio Pochettino).
- All of Son Heung-min's four goals were assisted by Harry Kane, the first time a player has assisted another player's hat-trick since May 2003, when Thierry Henry assisted Freddie Ljungberg's treble for Arsenal against Sunderland.
- Southampton striker Danny Ings has netted the opening goal in 11 Premier League games since the beginning of last season, more than any other player in the competition.
- Tottenham have failed to keep a clean sheet in their past 10 Premier League matches against Southampton, their worst run against a single side since 13 games without a shutout between May 2001 and May 2018 versus Leicester City.
- Spurs forward Harry Kane is only the sixth player to assist four goals in a single Premier League game, and the first English player to do so. Indeed, Kane only assisted two league goals in the entirety of last season.
- Spurs team-mates Son Heung-min and Harry Kane have combined for more Premier League goals than any other duo in the competition since the Korean's move to England in August 2015 (24 goals).
- Tottenham's Harry Kane is the first player to be directly involved in five goals in one Premier League game (one goal, four assists) since Mohamed Salah versus Watford in March 2018 (four goals, one assist). It is also the second time Kane has managed to do so (also May 2017 versus Leicester).
Southampton travel to Burnley in the Premier League on Saturday (20:00 BST) while Tottenham are at Leyton Orient in the Carabao Cup on Tuesday (18:00 BST).
- 5StephensBooked at 68mins
- 3BertrandBooked at 44mins
- 17S ArmstrongSubstituted forTellaat 68'minutes
- 6RomeuBooked at 5minsSubstituted forSmallboneat 55'minutes
- 10AdamsBooked at 39minsSubstituted forLongat 80'minutes
- 2DohertyBooked at 79mins
- 6D Sánchez
- 28NdombeleBooked at 45minsSubstituted forLo Celsoat 45'minutesBooked at 90mins
- 27Lucas MouraSubstituted forLamelaat 61'minutes
- 10KaneSubstituted forBergwijnat 84'minutes
- 7Son Heung-Min
- 18Lo Celso
- David Coote
- Shots on Target
Second Half ends, Southampton 2, Tottenham Hotspur 5.
Corner, Tottenham Hotspur. Conceded by Jan Bednarek.
Attempt blocked. Giovani Lo Celso (Tottenham Hotspur) left footed shot from outside the box is blocked. Assisted by Steven Bergwijn.
Giovani Lo Celso (Tottenham Hotspur) is shown the yellow card.
Moussa Djenepo (Southampton) wins a free kick on the left wing.
Foul by Giovani Lo Celso (Tottenham Hotspur).
Foul by Shane Long (Southampton).
Eric Dier (Tottenham Hotspur) wins a free kick in the defensive half.
Nathan Tella (Southampton) wins a free kick in the defensive half.
Foul by Ben Davies (Tottenham Hotspur).
Goal! Southampton 2, Tottenham Hotspur 5. Danny Ings (Southampton) converts the penalty with a right footed shot to the centre of the goal.
VAR Decision: Penalty Southampton.
Penalty conceded by Matt Doherty (Tottenham Hotspur) with a hand ball in the penalty area.
Nathan Tella (Southampton) wins a free kick on the right wing.
Foul by Steven Bergwijn (Tottenham Hotspur).
Attempt saved. James Ward-Prowse (Southampton) right footed shot from outside the box is saved in the top right corner.
Nathan Tella (Southampton) wins a free kick in the attacking half.
Foul by Steven Bergwijn (Tottenham Hotspur).
Substitution, Tottenham Hotspur. Steven Bergwijn replaces Harry Kane.
- Kitchen Starter Pack: Delicious recipes and food hacks that won't break the bank
- BBC Food: How well do you know your coffee?