Nathan Broadhead came off the bench to head home a stoppage-time winner and send Alex Neil’s side back into the League One play-off places.
The striker had missed the team’s last three matches with a hamstring injury but made the difference against a compact Gills defence.
Sunderland now have six games remaining as they try to secure a play-off place.
Our chief SAFC writer Phil Smith has delivered his verdict on how each Black Cats player fared at the Stadium of Light:
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9. Alex Pritchard - 6
Probably Sunderland’s most persistent attacking threat on a largely encouraging return from injury. Completed 70 minutes seemingly without complaint, which is a bonus moving forward. 6 Photo: JPI Media
10. Jack Clarke - 5
Started brightly and played one very good cross for Luke O’Nien but ultimately found himself running into traffic too often. Persistent in his willingness to show for the ball. 5 Photo: FRANK REID PHOTOGRAPHER 2022
11. Ross Stewart - 5
Battled hard but got little out of Gillingham’s defence. Not quite at his sharpest in the box. 5 Photo: JPI Media
12. Elliot Embleton (sub) - 8
Got into some good areas and showed for the ball when his side were running out of ideas. The cross for Broadhead was a stunner, and a massive moment in Sunderland’s season. 8 Photo: JPI Media