If you had told Southampton manager Claude Puel at the beginning of the season that his defence would prove a problem area, he would probably have been surprised. But with Jose Fonte wearing West Ham colours yesterday following his £8m move last month and Virgil Van Dijk out for three months with an ankle injury, Saints' rear-guard suddenly has a soft centre and West Ham took full advantage.

It had all started so well for Puel's men when Italy forward Manolo Gabbiadini, their £14m new signing from Napoli, scored after only 12 minutes of his debut. But Andy Carroll levelled only two minutes later and Pedro Obiang put the Hammers in front with his first goal for the club on his 55th appearance in all competitions. An own goal by the normally dependable Saints captain, Steve Davis made it 3-1 early in the second half and although Saints did their best to get back into the match, they found West Ham as steady at the back as they themselves used to be.

Slaven Bilic, the West Ham manager, has spoken on the eve of the match of wanting to increase his team's one-point advantage over Saints and will have enjoyed doing so, especially after Southampton's 3-0 victory when the two teams met in London in September. His only concern will be the need to withdraw the injury prone Carroll after less than an hour.

Obiang pulled West Ham level (Getty)

Carroll had just finished complaining to referee Graham Scott that he had been obstructed by Maya Yoshida as he went for a header when Gabbiadini announced his arrival in Hampshire in style. A simple lofted pass sent the Italian clear of defenders down the left and, with West Ham far too slow to realise the danger, he ran into the penalty area, took a look up and crashed the ball in off the crossbar from an unlikely angle. Fonte was closest to recovering but not close enough, and at that point he might have wondered whether he was in for an uncomfortable afternoon on his return to the club he captained until recently.

But Southampton's defence was unable to hold the lead for long. Within two minutes, Obiang slipped the ball between Yoshida and Jack Stephens to Carroll, who powered into the area and finished with an emphatic low shot.

And the visitors could have led before the interval. Carroll helped create a chance just short of the half-hour when he ducked under a cross from stand-in right back Cheikou Kouyate to allow Aaron Cresswell to collect the ball and hit a fierce volley that was saved by Fraser Forster. Then Forster had to be alert to gather a diagonal pass from Robert Snodgrass before Sofiane Feghouli could reach it.

Carroll scored the second for the Hammers (Getty)

Saints' unconvincing central defenders almost gifted West Ham a second goal five minutes before half time. Stephens mistimed his jump to allow Cresswell's cross to drift over his head and Yoshida swung and missed the ball. Feghouli pounced but instead of shooting he tried to go the long way round Ryan Bertrand and took the ball out of play.

But they were ahead anyway after 44 minutes. Southampton cleared a corner kick from the left as far as Obiang, 35 yards out. That, by itself, should not have posed a problem bearing in mind the midfield player's non-existent scoring record in English football. But he was allowed to advance unchallenged and hit a 25-yard daisy-cutter that somehow found its way past everyone including Forster and into the bottom far corner.

Southampton looked for a reply but Darren Randolph was down quickly to his right to push away an 18-yarder from James Ward-Prowse. And Randolph denied the Southampton midfield player again soon after the restart as he tried a cheeky shot to the near post from a free kick on the left.

Winston Reid did well to block a shot from Gabbidini after Ryan Bertrand had taken a pass from substitute Nathan Redmond and crossed low, and West Ham went up to the other end to make it 3-1. Snodgrass was sandwiched by two defenders on the left and when Mark Noble flighted the free kick to the near post, Davis swung a lazy boot at the ball and deflected it past Forster.

Gabbiandini scored on his debut for Southampton (Getty)

Saints had to take risks now and they should have reduced the arrears after 59 minutes when Kouyate, unsighted by the leap of Fonte, could only head an attempted clearance to the feet of Gabbiadini but he shot hurriedly and swept the ball over the crossbar.

But the chances continued to come for the home side. Randolph tipped a header by Ward-Prowse over the bar and from the corner kick, Michail Antonio nodded Yoshida's header off the line. Then Randolph did well to hold Davis's piledriver with two forwards rushing in case of any slip. Next Davis's clever reverse pass allowed Redmond to cross, but Yoshida, attempting an acrobatic overhead kick, showed why he is a defender and not a forward.

Line ups:

Southampton (4-3-3): Forster; Cedric, Stephens, Yoshida, Bertrand; Ward-Prowse, Romeu, Davis; Boufal (Long 64), Gabbiadini; Rodriguez (Redmond ht).

Substitutes not used: Taylor, Clasie, Gardos, Hojbjerg, McQueen.

West Ham United (4-4-2): Randolph; Kouyate (Collins 71), Fonte, Reid, Cresswell; Feghouli (Calleri 90), Obiang, Noble, Snodgrass; Carroll (Lanzini 56), Antonio.

Substitutes not used: Adrian, Fletcher, Fernandes, Quina.

Booked: Cresswell, Reid