Having seen Andrew Frampton sent off in the closing minutes at Spotland, Martin Allen's visitors could consider themselves fortunate to take anything from the clash.
The Gills found themselves a goal down after 12 minutes and had only themselves to blame. A defensive mix up between Gills defender Leon Legge and goalkeeper Stuart Nelson saw the ball drop invitingly for George Donnelly and the Dale forward hooked a fine finish into the unguarded net from 25 yards.
The visitors turned up the heat with a spell of pressure early in the second half which saw Danny Kedwell go close twice. His first effort, blasted at goal from a tight angle, was saved by Josh Lillis. Minutes later he saw a glancing header bounce inches wide of the post.
But it was third time lucky for the frontman when Matt Fish delivered an inviting cross from the right flank into the six-yard box, Kedwell making no mistake with his headed finish.
Rochdale finished strongly and Gillingham were reduced to 10 men for the last eight minutes of the match after Frampton was dismissed having clashed with Grant over a poor challenge by Donnelly on Legge.