Southampton held on to an early goal from Maya Yoshida to edge out West Ham 1-0 despite Victor Wanyama's red card.
Saints had to play for the majority of the second half with 10 men after Wanyama's dismissal - his third of the season - for a tackle on Dimitri Payet.
But West Ham could not find a way past a Saints rearguard which has now kept five consecutive clean sheets, with goalkeeper Fraser Forster yet to concede in seven and a half hours since he returned from a long-term injury.
In truth Forster had little to do, although when he was called upon to keep out a powerful Winston Reid header, he was equal to the task.
West Ham keeper Adrian was straight into the action, by contrast, and he pulled off a fine point-black save to keep out Cedric Soares' header from Shane Long's cross.
Yoshida's goal came in the ninth minute after the visitors failed to deal with a corner. Wanyama charged into the area and prodded the ball into the path of Yoshida to sweep past Adrian from close range.
West Ham claimed they should have had a penalty when Yoshida clipped Enner Valencia's heels but referee Mark Clattenburg was not convinced.
Forster came to Saints' rescue on the half-hour mark with a superb reflex save, palming out Reid's goalbound header.
New Zealand defender Reid then glanced another header narrowly over the crossbar from Payet's corner.
Payet was starting to exert his influence after the break when, in the 53rd minute he skipped away from Wanyama in the centre-circle only to be chopped down from behind by Saints' midfield enforcer.
The challenge enraged Hammers boss Slaven Bilic, who had seen his key playmaker sidelined for three months by a similar tackle by Everton's James McCarthur earlier in the season.
Clattenburg took his time to make a decision, initially appearing to reach for a yellow card, but he eventually settled on a straight red as the former Celtic midfielder pleaded his innocence.
Long could have doubled Saints lead just after the hour when James Collins misjudged Forster"s long clearance only to blaze his shot over the crossbar.
West Ham's new signing Emmanuel Emenike almost made a name for himself moments after coming on as a substitute, but he headed Sam Byram's cross wide.
In stoppage-time West Ham appealed for another penalty after Collins' shot hit Jose Fonte's arm, but it was not to be their day.