Charlie Austin, Dusan Tadic and James Ward-Prowse were all on the scoresheet as Southampton recorded a 3-0 victory over West Ham United in Sunday afternoon's Premier League clash at the Olympic Stadium.
The Hammers have now lost five of their six league matches this season, with that run of form leaving them 18th in the Premier League table on three points, while Southampton have jumped into 10th spot.
Inside an atmospheric stadium, it was West Ham that had the first half-chance inside three minutes, but on-loan Juventus striker Simone Zaza could only fire wide of the post after collecting a long pass on his chest.
Southampton, who entered the match off the back of three straight wins in all competitions, were a serious threat on the counter-attack, however, and Pierre-Emile Hojbjerg should have done better when presented with time and space inside the West Ham box in the ninth minute of action.
The home side had two separate penalty calls inside the opening 20 minutes and both involved Southampton defender Cedric, but referee Jonathan Moss was not interested, much to the frustration of the vocal West Ham fans.
Chances were extremely few and far between as the first period continued to gather pace in the capital, with a couple of free kicks into both boxes about as close either side came to making the breakthrough inside the first 30 minutes of football.
The first serious opportunity of the match arrived 10 minutes before the interval when Zaza's near-post header from a corner looked to be falling perfectly for Michail Antonio, but the Englishman could not make contact and Southampton managed to clear their lines.
It was the visitors that made the breakthrough in the 40th minute, however, when Ryan Bertrand found space down the left before delivering a cross in to Austin, who scuffed the ball into the bottom corner.
Southampton had two good opportunities to score a second in the final minutes of the first period as West Ham continued to struggle, but Hammers goalkeeper Adrian got down to keep out a strike from Nathan Redmond, before Cedric missed the post from close range.
West Ham boss Slaven Bilic made one alteration at the break as Sofiane Feghouli, who joined the club from Valencia in the summer, replaced Manuel Lanzini in a wide midfield role as the Hammers looked for more inspiration in the final third of the field.
It was Southampton that started the second period the brighter, however, and Adrian had to keep out a Jose Fonte header in the 51st minute, before the Spaniard made an even better stop to deny Tadic from close range moments later.
The Saints continued to threaten though and had their second just past the hour when Austin found Tadic in the final third, and the attacker gave Adrian the slip before rolling the ball into an empty net to stun the London Stadium into silence.
The visitors were rampant and could have scored a third five minutes later when Redmond found Steven Davis on the edge of the West Ham box, but the Northern Ireland international missed the target, before having a goal-bound strike blocked by Havard Nordtveit moments later.
West Ham came back and had two excellent chances of their own 15 minutes from time, but Dimitri Payet saw his goal-bound strike blocked, before firing a low effort wide of the post in another Hammers attack. Zaza also came close for the hosts as the pressure continued, only for Virgil van Dijk to clear off the line.
In the end, it was Southampton that scored the game's third goal - Ward-Prowse tapping home from close range in the second minute of additional time as the Saints made it four straight wins in all competitions.
Next up for West Ham is a home game against Middlesbrough next Saturday, while Southampton will travel to Hapoel Be'er Sheva in the Europa League on Thursday night before visiting the champions Leicester City in the league next Sunday afternoon.
