Hal Robson-Kanu's second-half thunderbolt completed a fine comeback victory for West over a below-par Southampton at St Mary's to move Tony Pulis' side up to eighth in the Premier League.
Shane Long's near post header against his former club gave the Saints the lead after 41 minutes, but their advantage lasted barely 50 seconds.
Claudio Yacob and Chris Brunt exchanged passes before a flick-on from Hal Robson-Kanu allowed Matt Phillips to side-foot into the bottom corner.
Robson-Kanu - who has sat on the bench for all 14 games since joining the club - took advantage of uncertainy at the heart of the Saints defence to smash an unstoppable shot for his first goal since scoring for Wales against Belgium at Euro 2016.