A brilliant first-time volley from Jermaine McGlashan gave the hosts a deserved lead before Marlon Pack calmly side-footed a second, and the points were wrapped up six minutes from time when Steve Elliott stroked the ball home from 12 yards after Millers 'keeper Andy Warrington had fumbled a corner.
Evans said: "We had a lot of good possession in the first half but didn't do anything with it.
"Every single one of their goals came from individual errors. It's not acceptable and there are no excuses. We just need to get back on the training ground and work hard again.
"We had plenty of possession in the first half, the stats would have been staggering, but we've overplayed on a pitch that is shocking and not good for football.
"Goals always change games but I can't remember us having to force their 'keeper into a proper save. We didn't get the ball into the box - we wanted to play five-a-side until we realised it is an 11-a-side game.
"They (Cheltenham) put balls in the box at every opportunity - we've been beaten by a good side.
"Our performances have been solid so we need to take this blow, work hard and come back strong again."