Jordy Clasie scored his first Premier League goal as Southampton extended their unbeaten run to three matches at the expense of West Bromwich Albion.
Clasie struck from a cross by Dusan Tadic, who was set up by Shane Long.
Fraser Forster ensured that the Baggies failed to score for the fifth time in six matches with some impressive saves.
He denied James Morrison and Salomon Rondon in the first half and in the dying stages kept out a Craig Dawson volley and a Jonny Evans effort.
Southampton move three points clear of Watford in ninth and four behind eighth-placed West Brom, with two matches in hand.