Tom Flanagan scored the winner against his former club as 10-man Sunderland came from behind to beat Gillingham 2-1 at Priestfield.
The Gills started brightly, with Jack Tucker forcing Sunderland goalkeeper Ron-Thorben Hoffmann into a save after seven minutes.
Steve Evans' side took the lead in the 25th minute, as Danny Lloyd fired home from the penalty spot after Luke O'Nien tripped Stuart O'Keefe in the box.
Sunderland equalised against the run of play three minutes into first-half stoppage time as Aiden O'Brien capitalised on poor defending from Max Ehmer to poke home Dan Neil's cross.
Flanagan, who was a part of Gillingham's League Two title-winning team in 2012-13, completed the turnaround as he headed in from Alex Pritchard's delivery nine minutes into the second half.
The visitors played the final 23 minutes with 10 men after referee Lee Swabey sent off Elliot Embleton for a sliding tackle on Tucker.
Lee Johnson's side stood firm as Callum Doyle's block denied John Akinde, and Hoffmann kept out Robbie McKenzie's looping goal-bound header.