Peter Odemwingie increased the pressure on Southampton boss Nigel Adkins as his two goals gave West Brom a 2-0 win and moved them into fifth spot in the Barclays Premier League.
Adkins' side remain rooted to the foot of the table after a fifth successive away defeat and they have now conceded 28 goals in 10 league matches.
But these are halcyon days for the Baggies and they bounced back from heartbreaking injury time defeats against Manchester City and Newcastle thanks to a goal in each half from Odemwingie.
It was their fifth victory in six home matches and, although not at their best, they still contained too much firepower for the Saints. Although the visitors showed plenty of promise in spells, their leaky defence is undermining their attacking threat.
Rickie Lambert had the first attempt on goal and his low drive from a narrow angle contained plenty of power but was held onto by West Brom keeper Ben Foster.
But the home side soon started to look more threatening and it needed a last ditch tackle from Morgan Schneiderlin to deny Long after Jonas Olsson had headed a Graham Dorrans free-kick back across goal.
Odemwingie flashed a low 25 yard shot inches wide in a swift Albion counter-attack after Foster had gathered Lambert's header from a Gaston Ramirez centre. But the Nigeria international broke the deadlock in controversial fashion in the 36th minute.
The impressive Mulumbu released Odemwingie whose left-footed shot contained plenty of power but took a deflection off Maya Yoshida as it flew past Saints keeper Paulo Gazzaniga. But TV replays also showed that Odemwingie had appeared to handle the ball in the build-up.
Southampton started the second half on the offensive and a shot on the turn from Lambert struck the bar with Foster well beaten. But after 60 minutes Odemwingie doubled Albion's lead with a clinical finish.
Left-back Liam Ridgewell's long pass found Long who held the ball up, cut inside and floated over an inviting centre which Odemwingie headed home from close range to seal the win.