Substitute Joe Rothwell scored a late double as Southampton survived a Sunderland fightback to keep their slim hopes of automatic promotion back to the Premier League alive.
The Saints, who had their midweek game against Preston postponed at late notice because of a fire on a nearby industrial estate, took an early lead when Stuart Armstrong scored on the rebound after Anthony Patterson had saved Jan Bednarek's header.
Adam Armstrong made it 2-0 in controversial circumstances from the penalty spot. The former Newcastle man slipped as he took his shot and appeared to strike the ball twice but referee Stuart Atwell allowed the goal to stand despite Sunderland protestations.