It wasn't a good night for former boss Steve Evans who saw his team conceed 5 and have a man sent off as the Millers 2nd half performance blew the Gills away...
The table-toppers conceded an early goal but comfortably rallied to brush aside former boss Steve Evans' side.
The visitors took a fifth-minute lead with Olly Lee turning in emphatically from Ryan Jackson's right-wing centre.
The leveller came in the 38th minute through Freddie Ladapo, who bundled in after a mix-up from a long punt upfield.
Rotherham ensured they went in at the break ahead with Mickel Miller volleying in from the edge of the box on 45 minutes.
The third came in the 59th minute with Rotherham awarded a penalty after Michael Ihiekwe was pulled down in the box. Dan Barlaser smashed past Aaron Chapman.
Barlaser was given another chance to score from the spot but this time he blasted against the bar after Jackson was shown a second yellow card for hauling down Chiedozie Ogbene.
The midfielder did get his second on 81 minutes after lashing in on the angle from Joshua Kayode's pass.
Ogbene rounded off the scoring in the 89th minute with a stunning strike from the edge of the box.