Phil Parkinson made six changes to the side that lost at home to Burton Albion 10 days ago, and switched to the same three-at-the-back system he used against Gillingham at the Priestfield Stadium in the FA Cup replay last month.
Tom Flanagan replaced Joel Lynch in central defence, with fellow centre-back Alim Ozturk coming came into the side in place of wideman Aiden McGeady to enable the change of shape.
Laurens De Bock was preferred to Denver Hume in the left wingback role, while Jon McLaughlin replaced Lee Burge in goal.
George Dobson returned from suspension to take the place of Max Power, who was serving a one-match ban after accumulating five yellow cards.
And Marc McNulty returned from injury up front, taking the place of Duncan Watmore alongside Will Grigg.
Charlie Wyke was back in the squad after six weeks out of action and he was included on the bench.
Gillingham boss Steve Evans named the same starting XI which beat Doncaster in the FA Cup in midweek.
Former Sunderland youngster Mikael Mandron started up front for the Gills.
You can follow all the action from Priestfield in our with post-match analysis and reaction.
Sunderland: J McLaughlin, Willis, Ozturk, Flanagan, C McLaughlin, O'Nien, Leadbitter, Dobson, De Bock, Grigg, McNulty
Subs: Burge, Hume, Lynch, McGeady, Maguire, Watmore, Wyke.
Gillingham: Bonham, Fuller, Ehmer, Tucker, Ogilvie, Jones, Byrne, Lee, O'Connor, Hanlan, Mandron.
Subs: Walsh, Hodson, Ndjoli, Charles-Cook, Cisse, Marshall, Jakubiak.
