Former Millers favourite Deon Burton did the damage with a goal in each half.
Rotherham staged a game fightback, had two penalty claims turned down and
hit the woodwork, but had to be content with Jason Taylor's 69th minute consolation.
"This was a big game for us," said Evans, "But if this was the benchmark we have shown we can beat that benchmark.
"Some of the stuff that went on in the match I am surprised it remained 11 v 11, as probably do most people in the ground, but if we play like this every week we will win promotion. We were fantastic.
"A couple of Gillingham's back room team have admitted to me that they rode their luck. That's the biggest understatement I've ever heard."
And Evans hit out at the challenge from Burton that forced home skipper Ian Sharps off injured after 15 minutes.
"It was a nasty, horrible vindictive challenge," he said. "It deserved a straight red but the referee missed it.
"We'll look at the DVD and if its as bad as we think it is I'll send it to the Football League."