Rowe on target for Town, but fall to defeat at Priestfield Stadium
Town suffered defeat for the first time this pre-season, despite Danny Rowe's late consolation goal.
Tom Eaves scored from the spot and Scott Wagstaff netted a beauty as Mick McCarthy's side were beated in Kent.
The Blues shaded the opening 45 minutes, and had it not been for a combination of goalkeeper and defender, Joe Garner would have added to his five pre-season goals.
Garner, who joined from Rangers in June, seen his initial shot saved by Tomas Holy, before the follow up was cleared off the line by a Gills defender.
Town came close again soon after through Kevin Bru after he had linked up well with Grant Ward, but the Mauritian was denied by Holy.
Bartosz Bialkowski, who was returning in goal having missed Tuesday's win at Peterborough through illness, had little to do in the first-half, but had to be alert to claw Eaves' goalbound lob behind for a corner.
The Pole could do little with the opener, however, as Eaves stepped up to send him the wrong was from the spot after Luke Chambers was adjudged to have fouled former Blue Lee Martin in the box early in the second-half.
Blues boss, Mick McCarthy made wholesale changes midway through the second-half, with all ten outfield players substituted.
Those changes couldn't prevent the Gills doubling their lead soon after, as Scott Wagstaff cut inside and curled a brilliant effort past Bialkowski and into the far corner.
Danny Rowe did pull one back for Town as he nodded in Conor McKendry's cross at the back post, but it was to be no more than a consolation as the Blues fell to a 2-1 loss.
Town: Bialkowski, Spence (Iorfa, 70), Chambers (C. Smith, 70), T. Smith (Webster, 70), Knudsen (Kenlock, 70), Ward (Rowe, 64), Bru (McDonnell, 70), Downes (Nydam, 70), Celina (McKendry, 70), Sears (McGoldrick, 70), Garner (Morris, 70).