Marc Antoine-Fortune gave the Baggies a dream start after turning home from close range on six minutes.
Here, Sports Mole dissects a superb away victory for Steve Clarke's side at St Mary's.
On target 4
On target 9
Was the result fair?
West Brom fully deserved to claim all three points after showing a ruthless streak in the final third to match a resolute defensive display. Saints failed to cope with the pace and power of Lukaku all afternoon and despite making changes early in the second half were well beaten.
The Saints produced easily their worst performance since Mauricio Pochettino took charge, failing to create chances or prevent them at the other end. Rickie Lambert was starved of service for long spells, while Artur Boruc was often left without support by slack marking from set pieces. Nathaniel Clyne's forward bursts were a rare bright spot for the home side, who kept possession without ever threatening a physical West Brom rearguard.
West Brom's performance
Clarke can be delighted with his side's efforts this afternoon in a display much more in line with their early-season form. Jonas Olsson and Gareth McAuley were strong in defence, while Graham Dorrans showed off his full range of distribution in an accomplished midfield display. Lukaku, Fortune and Long continually broke with pace and purpose, making the Baggies value for their eye-catching win.
Sports Mole's man of the match
Romelu Lukaku: The Belgian was magnificent this afternoon, giving Jos Hooiveld a torrid time with physical, measured approach play throughout. The Belgian powerhouse took his goal with a predator's instinct before sliding a clever pass to Long for the third and final strike. On this evidence Chelsea will have some player on their books next season, thanks largely to his continued development at The Hawthorns.
Ramirez will have to take this unwanted accolade this afternoon, just ahead of a collectively shoddy Saints defence. The Uruguayan's petulant elbow caught Long in the face with the referee just yards away, effectively ending his side's chances of mounting a late comeback.
Robert Madley was in the thick of the action on his Premier League debut, issuing three red cards in the second half after a relatively quiet first 45 minutes. In fairness to the 27-year-old, he was left with little choice on all three occasions. Ramirez and Fortune were both guilty of violent conduct, while Fox's late lunge on Reid was poorly timed and dangerous.
Southampton: Pochettino will need to lift his troops next weekend as they take on a Tottenham Hotspur side chasing Champions League qualification at White Hart Lane.
West Brom: The Baggies will aim for successive wins when relegation-haunted Wigan Athletic visit the Midlands next Saturday.