Sunderland still have work to do to seal a place in the Sky Bet League One play-offs after promotion rivals Blackpool secured a 1-0 win at the Stadium of Light.
Sullay Kaikai's stunning volley in the 56th minute was enough to secure the fifth-placed Seasiders three points that enhance their own top-six credentials.
But the defeat for out-of-sorts Sunderland means that Lee Johnson's side, who sit fourth, are yet to guarantee a top-six finish because of their recent slump.
The Black Cats, who have fallen out of contention for the automatic promotion spots with a seven-match winless run, sit five points above seventh place with two games left.
There were very few chances in the first half. The nearest Sunderland came was when Aiden O'Brien's outstretched boot directed Grant Leadbitter's through pass to goalkeeper Chris Maxwell.
Blackpool striker Jerry Yates stung the palms of goalkeeper Lee Burge at the other end with five minutes of the half remaining. That was all they could muster.
After the restart, and a change of system, there were a few more chances with Charlie Wyke having three downward headers saved brilliantly by Maxwell.
And with 34 minutes remaining Blackpool went ahead when Kaikai struck the sweetest of volleys from a half-cleared corner inside Burge's left-hand post.
Sunderland's Lynden Gooch had a late effort fly wide.