Christian Eriksen scored twice as Tottenham maintained their challenge for a top-four finish and deepened Sunderland’s relegation worries.
Patrick van Aanholt gave the Black Cats the lead against the run of play but Eriksen levelled as Lee Cattermole failed to clear on the goalline.
Mousa Dembele fired Spurs ahead before Eriksen’s 25-yard shot deflected in off Sunderland debutant Jan Kirchhoff.
And Harry Kane converted a penalty after Kirchhoff fouled Danny Rose.
Tottenham move a point behind third-placed Manchester City before Manuel Pellegrini’s side play Crystal Palace at 15:00 GMT, while Sunderland remain in the Premier League relegation places.
Southampton 3 0 West Bromwich Albion
Ward-Prowse 5′, 35′ (pen) Tadic 72′
FT 90 +4
HT 2-0
Southampton followed up their midweek victory over Watford with a convincing home win against West Brom.
James Ward-Prowse scored a brilliant 25-yard curled free-kick and a penalty for his first goals of the season as Saints cruised into a half-time lead.
West Brom boss Tony Pulis made two attacking changes at the break but the home side remained in charge.
Serbian forward Dusan Tadic sealed the three points from a tight angle after a clever pass from Matt Targett.
Ronald Koeman’s Southampton move up to 10th in the Premier League table, while the Baggies stay 13th.
For other Premiership results see here