Two goals from Morgan Schneiderlin and a late Graziano Pelle strike saw Southampton come from behind to beat West Ham 3-1 at Upton Park.
Frenchman Schneiderlin, who handed in a transfer request earlier in the summer, twice profited from some sloppy Hammers defending to put the visitors on their way to three points they thoroughly deserved.
The midfielder curled in a sweet left-footer on the stroke of half-time to cancel out Mark Noble’s deflected effort then put the visitors ahead on 69 minutes when the Hammers fell asleep at a corner, allowing him to turn in James Ward-Prowse’s cross at the near post.
The points were made safe seven minutes from time when Pelle got his reward for a fine centre-forward display, smashing in from close range after Adrian could only parry Nathaniel Clyne’s cross into his path.
The third goal sparked a rush to the exits for the home fans, following a second home defeat in the space of a week for manager Sam Allardyce whose team were knocked out of the Capital One Cup on penalties by Sheffield United.
Southampton, who won at Millwall in the cup, started brightly as Pelle and Shane Long, a £12million signing from Hull, stretched the Hammers' defence.
West Ham paraded new loan signing Alex Song, the former Arsenal man joining from Barcelona, before kick-off, but took time to get into any sort of passing rhythm against the well-organised Saints.
It was 20 minutes before the home side were able to create an opening.
A free-kick from Stewart Downing was only half cleared, with the ball dropping back to the far post through a crowded six-yard box where Ricardo Vaz Te turned it goalwards. However, Saints goalkeeper Fraser Forster somehow made a reaction save with his leg at point-blank range to push the ball wide across the face of goal.
There was, though, little the former Celtic number one could do a few moments later to prevent West Ham taking the lead in the 27th minute.
Noble robbed Schneiderlin and drove towards the edge of the Saints penalty area. He let fly from 25 yards, with the ball deflecting off the boot of Maya Yoshida and into the far corner, just out of Forster's reach.
Southampton looked to make a quick response, with a deep cross from the left glanced down by Pelle, which Aaron Cresswell guided off the line.
To their credit, the visitors continued to stay composed despite now having to chase the match, with West Ham dropping an extra man into a packed midfield to compensate.
Pelle missed his kick when Serbian midfielder Dusan Tadic found space on the left for another dangerous cross into the West Ham penalty area, which Winston Reid gratefully cleared.
Schneiderlin showed the Italian how it should be done when he equalised on the stroke of half-time. A free-kick on the left touchline was floated in by Tadic and flicked on to the far post, where Schneiderlin drilled it back goalwards. Although Joey O'Brien made a brave block, Schneiderlin latched onto the rebound and curled it inside the far post.
Saints went close to taking the lead at the start of the second half when a shot by Long at the edge of the penalty area was turned behind by Adrian.
Tadic then had the West Ham goalkeeper scrambling down to his right with a low shot from 18 yards, and Schneiderlin crashed the ball over from 10 yards following the corner.
Saints had the ball in the net again when Pelle converted a free-kick from Ward-Prowse at the far post, but was one of three players ruled offside - although the decision was a tight one.
Allardyce had seen enough, and made a double change on the hour, as Ravel Morrison and Mohamed Diame replaced Mauro Zarate and Vaz Te.
It was no surprise when Schneiderlin put the Saints ahead midway through the second half. A short corner caught West Ham asleep, with a cross from Ward-Prowse flicked home at the near post by the French midfielder, who wheeled away to celebrate in front of the away fans behind the goal.
West Ham needed inspiration from somewhere, and £12million Ecuador forward Enner Valencia was sent on with 11 minutes left, replacing the ineffective Carlton Cole.
However, Southampton made sure of the victory in the 83rd minute when Pelle smashed home after Adrian had palmed out a cross from Clyne. The boos rang out around the Boleyn Ground at full-time from those disgruntled fans who had stayed on.