Millwall effectively secured Sky Bet Championship football next season after former Sunderland forward Duncan Watmore’s second-half strike at the Stadium of Light earned a 1-0 win.
In a game of few chances, Watmore, who had only been on the pitch four minutes, pounced to deliver the crucial goal that earned the Lions a third successive win.
Sunderland, however, saw their own winless run on home soil extended to six matches dating back to February 10.
The hosts threatened first and Millwall goalkeeper Matija Sarkic had to get down low to hold a drive from teenager Chris Rigg after he danced his way through the visiting defence.
Bradley Dack then created a couple of openings for Dan Ballard with some pinpoint deliveries but neither found the target.
Jobe Bellingham headed over another corner kick when he looked like he could at least test the Sarkic, but Millwall survived.
The Lions were struggling to create anything until former Sunderland midfielder George Honeyman’s set-piece was headed off target by Zian Flemming.
In a bid to improve things, Sunderland’s interim boss Mike Dodds pushed Bellingham up front for the second half as part of the changes brought about by replacing Dack with Trai Hume.
And Hume, operating at right wing-back, had the first effort after the restart when he drove a couple of feet over Sarkic’s bar from 22 yards.
In another attempt to lift the tempo by Dodds, Abdoullah Ba and Adil Aouchiche were brought on for the last half an hour.
Soon after that Sunderland thought they had the lead when Ryan Leonard somehow got in the way to block Callum Styles’ goalbound effort from Ba’s cross.
And in the 71st minute Millwall made the hosts pay when Ryan Longman’s low cross from the right was met by substitute Watmore, who had darted ahead of his markers to flick inside Anthony Patterson’s near post.
Bellingham almost deflected Brooke Norton-Cuffy’s cross into his own net in stoppage time but Millwall had already done enough to secure a vital three points.