A 15 minute second half goal blitz saw forwards Nouha Dicko, Alex Revell and Kieran Agard (penalty) seal the points at Sixfields and push the Millers up to the fringes of the play-off places.
Evans spoke to the BBC press afterwards and said: "We came here under difficult circumstances. We've been robbed of Michael O'Connor late yesterday when he had to pull out with a thigh strain and Rob Milsom had to pull out with a back spasm in the warm up at half past 7.
"But Michael Tidser has come in for his first league start and in spells was the best player on the park, other than Dicky and Revs up front who were exceptional."
The gaffer added: "We knew it was going to be tough here and because we've beat them 3-0 that doesn't mean they're a bad side. They're a very good side and we've had to work very hard to beat them."