The Baggies jump ahead of Tottenham and Arsenal in the table with a competent display against the basement club as the Nigerian striker helped himself to two goals
Steve Clarke dropped striker Romelu Lukaku in favour of Shane Long whilst his opposite number brought the fit-again Gaston Ramirez back into the line-up in place of Jason Puncheon.
The Republic of Ireland striker justified the decision with an assist and a lively Peter Odemwingie scored both goals.
It was the Saints who started the brighter of the two and Rickie Lambert forced Ben Foster into a save with a first-time shot on the angle.
West Brom's first real chance of the game came after 19 minutes when Odemwingie burst down the right-hand channel before cutting in on his left and rifling a shot towards goal. The ball was going wide but was helped on its way by Zoltan Gera, who could only send it over the bar.
Long's first-time effort from a Youssuf Mulumbu pass flew into the crowd and Claudio Yacob dragged an effort wide as the game started to open up a little.
There was action at both ends of the pitch in the space of 30 seconds, Foster comfortably saving Lambert's header from a Ramirez cross before quickly throwing the ball out to Odemwingie.
The Nigerian burst down the right-hand channel before cutting in on his left and unleashing a fizzing shot that went just wide of the post.
Having just gone close with a left-footed drive, it was no surprise when Odemwingie finally did score by doing almost exactly the same again after 36 minutes.
He collected Mulumbu's pass before taking a touch and driving in from 20 yards out. The ball took a deflection of the unfortunate Jose Fonte, which took it past Paulo Gazzaniga and into the bottom corner.
The Saints' goalkeeper produced a fine save at the feet of Long when the Republic of Ireland striker was allowed a free run into the box. The rebound fell to Odemwingie but his shot was blocked wide.
Southampton went close a few minutes after the restart, Rickie Lambert smashing the bar on the half-volley as they went looking for the equaliser.
But it was the Baggies who got their noses further in front with a quick, counter-attacking move. Liam Ridgewell booted the ball down the channel, Long ran onto it and whipped an inviting cross into the box which Odemwingie headed in from close range on the hour mark.
The hosts were playing on the break more and more as the Saints pressed high up the pitch, only to be frustrated by some disciplined defending.
Lukaku, who came on for Long midway through the second half, caused Fonte a few problems. He played in fellow substitute Chris Brunt and his first-time effort just went wide of Gazzaniga's post.
There was no hat-trick for Odemwingie as manager Steve Clarke brought Marc-Antoine Fortune on as his replacement, allowing him to receive a standing ovation from a packed Hawthorns.
Maya Yoshida should really have pulled a goal back for the Saints but headed wide from a corner late on, and the Baggies comfortably saw out the victory.