Match ends, Tottenham Hotspur 1, Southampton 2.
Steven Davis scored twice as Southampton came from behind to beat second-placed Tottenham.
Home forward Son Heung-min chased a lost cause for the opener, gliding past Fraser Forster and coolly tucking the ball into an open net.
The visitors equalised through Davis, who slotted in under Hugo Lloris following Dusan Tadic's cut-back.
Spurs's Jan Vertonghen had a header cleared off the line, before midfielder Davis stroked in the winner.
Substitute Nacer Chadli could have saved a point for the hosts deep in stoppage time, but his poked effort was kept out by the big frame of Forster.
Having challenged for the Premier League title for most of the season, Tottenham now lie 10 points adrift of champions Leicester and are hanging on to second spot, two points ahead of local rivals Arsenal.
History repeating itself for Spurs
Manager Mauricio Pochettino has been praised this season for instilling in Tottenham a steeliness they had lacked in the past.
Nevertheless, having been the Foxes' closest challengers they have come up short, and dropping 20 points from winning positions - the most in the division - has clearly played a big part.
Arsene Wenger's Arsenal now have a chance to overtake Spurs and continue a run that has seen them finish above their north London rivals every season since 1995 - having missed out on the title, that would be a further, bitter blow.
The hosts did take the lead through South Korean Min's calm finish, but could not find a way past England international Forster thereafter.
The big goalkeeper got down quickly to save Christian Eriksen's effort in the first half and made a sharp stop off top scorer Harry Kane, who remains on 25 for the season.
Saints go marching on
The Premier League has been awash with remarkable stories this season. Leicester were shock winners, holders Chelsea produced a calamitous collapse, while Aston Villa finished bottom after a disastrous campaign.
Southampton, however, have every right to be considered one of the season's big success stories. Their 36 points in 2016 is only bettered by the tally of 41 from Claudio Ranieri's side, while they have already equalled their best ever Premier League total of 60, achieved under boss Ronald Koeman last term.
Saints' victory means they climb to sixth and are still in with a chance of a Europa League spot with one game remaining.
Centre-back Virgil van Dijk, who recently signed a new six-year deal, showed why there may be interest from bigger clubs with an accomplished performance to keep Kane at bay and 12 clearances in the match.
Victor Wanyama made his presence felt in the middle of the park, producing a match-high seven tackles and three interceptions, while playmaker Tadic has now been involved in eight goals in their last four games.
Man of the match - Virgil van Dijk
What they said:
Tottenham boss Mauricio Pochettino: "We are still in a great position and if we look back to the start of the season we all should be proud. We need to look at ourselves, not at our neighbour.
"We need to think like a big club, not worrying about what's happening in another house. We need to change that mentality, to be strong, to be a big club."
Southampton manager Ronald Koeman: "It's a great win for us, because to win here against Tottenham, one of the best teams in the league, is a big result.
"If we can win next week at home we will have 63 points - a really fantastic achievement by the team. We like to play in Europe, and it's important for the clubs and the players."
Tottenham will look to end the season on a high when they travel to Newcastle in their last game of the season on Sunday (15:00 BST), while Southampton end their campaign at home to Crystal Palace on the same day.
The stats you need to know:
- Tottenham have now recorded their highest tally of goals in a Premier League season (68).
- Son Heung-min scored in back-to-back Premier League games for the first time.
- Since he made his debut in August 2014, only Cesc Fabregas (25) and Mesut Ozil (23) have more Premier League assists than Dusan Tadic (19).
- Southampton midfielder Steven Davis netted his first ever Premier League double in this game.
- 8MasonSubstituted forChadliat 78'minutes
- 7Son Heung-MinSubstituted forN'Jieat 65'minutes
- 6José Fonte
- 17van Dijk
- 4ClasieSubstituted forRomeuat 58'minutesBooked at 74mins
- 10ManéBooked at 50minsSubstituted forPellèat 65'minutes
- 11TadicSubstituted forWard-Prowseat 86'minutes
- 7LongBooked at 83mins
- 2Cédric Soares
- Jonathan Moss
- Shots on Target
Second Half ends, Tottenham Hotspur 1, Southampton 2.
Attempt missed. Harry Kane (Tottenham Hotspur) left footed shot from outside the box is high and wide to the left. Assisted by Jan Vertonghen following a corner.
Corner, Tottenham Hotspur. Conceded by Fraser Forster.
Attempt saved. Nacer Chadli (Tottenham Hotspur) right footed shot from the centre of the box is saved in the bottom left corner.
Harry Kane (Tottenham Hotspur) wins a free kick on the left wing.
Foul by Jose Fonte (Southampton).
Attempt missed. James Ward-Prowse (Southampton) right footed shot from outside the box is close, but misses the top left corner. Assisted by Shane Long.
Danny Rose (Tottenham Hotspur) wins a free kick on the left wing.
Foul by Shane Long (Southampton).
Jan Vertonghen (Tottenham Hotspur) wins a free kick in the defensive half.
Foul by Graziano Pellè (Southampton).
Foul by Erik Lamela (Tottenham Hotspur).
Steven Davis (Southampton) wins a free kick in the defensive half.
Attempt blocked. Toby Alderweireld (Tottenham Hotspur) right footed shot from outside the box is blocked. Assisted by Christian Eriksen.
Corner, Tottenham Hotspur. Conceded by James Ward-Prowse.
Substitution, Southampton. James Ward-Prowse replaces Dusan Tadic.
Attempt missed. Shane Long (Southampton) right footed shot from the right side of the box is too high. Assisted by Graziano Pellè with a headed pass.
Attempt missed. Eric Dier (Tottenham Hotspur) header from the centre of the box misses to the right. Assisted by Kyle Walker with a cross.
Shane Long (Southampton) is shown the yellow card for a bad foul.