Felipe Anderson scored a quickfire double as West Ham came from behind to beat Southampton 2-1 and end the Premier League strugglers' winning run.
Ralph Hasenhuttl's appointment has turned around Southampton's fortunes in recent weeks, leading to back-to-back victories, but, despite Nathan Redmond's scrappy opener, they met their match in the form of West Ham's Brazilian winger.
Having netted a stunning equaliser 168 seconds after Redmond's goal, Felipe Anderson doubled his tally at the culmination of a slick counter-attack before the hour mark.
Lucas Perez should have wrapped up the win, but his failure to convert from close range ultimately mattered little as West Ham held firm to claim a third successive away win for the first time since September 2015.
Danny Ings prodded into the side netting as Southampton started in buoyant mood, though West Ham would have been ahead had Perez kept his cool from Aaron Cresswell's cut-back.
But it was after the interval that the game burst into life, when – with Lukasz Fabianski having pulled off a fine save – Redmond was able to bundle home, although it seemed that Southampton's attacker used his hand to get a vital touch.
Manuel Pellegrini's men wasted no time in responding, though, and were level inside three minutes as Felipe Anderson rifled home from the edge of the box.
And the turnaround was complete in the 59th minute, Felipe Anderson lashing high into the net after latching onto Michail Antonio's precise pass, although Southampton were adamant there was a foul in the build-up.
Jannik Vestergaard prevented Perez atoning for his earlier miss soon after, but that block was not enough to spark a comeback, as Hasenhuttl suffered his second defeat as Saints boss.
What does it mean? Saints remain in the mire
Thanks to Burnley's defeat on Boxing Day, Southampton had the chance to move clear of the relegation zone, but they remain just three points above the 18th-place Clarets.
West Ham, meanwhile, are up into the top half, level on points with Everton and one behind Leicester City in seventh.
Felipe Anderson's flare coming to the fore
Signed for a reported £36million from Lazio in July, Felipe Anderson struggled to settle in the opening weeks of the season but is now hitting his best form and his quality could well be enough to propel West Ham towards a push for European qualification.
Injuries mounting up for the Hammers
Despite the victory, Pellegrini will be hugely concerned over West Ham's extensive injury list, with nine first-team players missing Thursday's encounter. Indeed, Pellegrini named only six substitutes, rather than the seven that are allowed.
Key Opta Facts
- Southampton have dropped 15 points from winning positions in the Premier League this season; the most of any team in the competition, with 12 of those coming in home games.
- West Ham have won five of their last six games in the Premier League (L1) – their previous five wins in the competition came over a run of 20 games between April and November.
- This was West Ham's first Premier League away win after conceding the opening goal since May 2017, when they won 2-1 against Burnley at Turf Moor.
- Southampton have suffered back-to-back Premier League defeats against West Ham for the first time since October 2001.
- West Ham have won 15 points in the Premier League in December (P6 W5 D0 L1); their most in a single month of a season in the competition's history.
What's next?
Southampton bring 2018 to a close by hosting champions Manchester City, who will be looking to avoid a third straight defeat. West Ham, meanwhile, face Burnley.
