Manolo Gabbiadini made it three goals in two matches since signing for Southampton in their 4-0 win over Sunderland at the Stadium of Light.
Jermain Defoe had threatened early on for Sunderland, before Gabbiadini deflected in Ryan Bertrand's cross on 30 minutes.
The Italian finished brilliantly to make it 2-0 on the stroke of half-time and Southampton maintained their supremacy after the break.
Dusan Tadic went close before a Jason Denayer own goal and a late Shane Long strike confirmed the three points that lifted Southampton to 11th, while Sunderland remain bottom.
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