2015 ended in disappointment for Southampton as West Ham United came from behind to win 2-1 at the Boleyn Ground.
Second-half goals from former Saints loanee Michail Antonio and substitute Andy Carroll turned the game around after Carl Jenkinson had scored an own-goal in the 13th minute.
Saints had plenty of chances at 1-0 to extend their advantage, but Steven Davis, José Fonte and Oriol Romeu were all unable to convert and Saints were made to pay.
Ronald Koeman made two changes from the Boxing Day victory over Arsenal, with Jordy Clasie and James Ward-Prowse dropping to the bench.
Romeu replaced Clasie alongside Victor Wanyama in the midfield, while Tadić came in for Ward-Prowse as Saints reverted to their more familiar 4-2-3-1 formation.
There was also a 250th club appearance for Saints captain José Fonte as he lined up at the heart of a defence looking to make it back-to-back clean sheets for the first time since early November.
The Hammers – who came into the game on the back of five straight draws in the Barclays Premier League – started brightly, but it was Saints who grabbed the opening goal.
Steven Davis played in Shane Long down the left-hand side and his cross was turned past his own goalkeeper by Jenkinson under pressure from Tadić.
Saints, buoyed by the win against Arsenal and the early goal, were well on top during the opening 30 minutes and were perhaps unlucky not to be two goals ahead.
Long was again the provider as he cut the ball back for Davis, but the midfielder’s shot was deflected just over the bar by James Collins.
The Northern Ireland captain then won possession back 40 yards from goal and ignored options to his right and left to go himself, but watched as his strike flew just wide of the far post.
There was still time before the break for Fonte and Tadić to have efforts denied by good saves from Adrian as the Hammers struggled to cope with Saints.
The hosts made a double change at the break and one of those substitutes should have equalised. After Cuco Martina had cleared a header off the line from Collins, Carroll fired over the bar from close range.
The equaliser came with 20 minutes remaining. Antonio cut in from the left and after going to ground saw Wanyama's clearance deflect off his head and loop over Maarten Stekelenburg.
With the home fans lifted following the equaliser, the Hammers continued to press and took the lead with ten minutes remaining. After Antonio had headed against the bar, Carroll was on hand to apply the finishing touch from close range.
Antonio almost made it 3-1 late on, but the Hammers had done enough to condemn Saints to defeat in their final game of 2015.
West Ham United: Adrian; James Collins, Angelo Ogbonna, James Tomkins, Carl Jenkinson; Mark Noble (c), Cheikhou Kouyate, Alex Song (Manuel Lanzini 46); Michail Antonio, Mauro Zarate (Andy Carroll 46), Enner Valencia (Pedro Obiang 86).
Unused substitutes: Darren Randolph (GK), Stephen Hendrie, Reece Oxford, Josh Cullen.
Goals: Michail Antonio (69), Andy Carroll (79)
Booked: James Tomkins (58)
Southampton: Maarten Stekelenburg; Cuco Martina (Maya Yoshida 70), José Fonte (c), Virgil van Dijk, Ryan Bertrand; Oriol Romeu, Victor Wanyama; Dušan Tadić (Juanmi 75), Steven Davis, Sadio Mané (Gastón Ramírez 75); Shane Long.
Unused substitutes: Paulo Gazzaniga (GK), Jordy Clasie, James Ward-Prowse, Steven Caulker.
Goal: Carl Jenkinson (own-goal 13)
Booked: Cuco Martina (52), Oriol Romeu (56), Ryan Bertrand (66)
Referee: Michael Oliver