Adam Le Fondre was again the hero as he netted his 15th and 16th goals of the season as the Millers comfortably took the points.
Le Fondre opened the scoring after a slow start to the afternoon on 26 minutes, as he composed himself to finish off a one on one with 'keeper Clarke after Marcus Marshall's shot was blocked by Ben Futcher.
And it was 2 before the break as Alfie netted a second, firing home left footed into the corner following good link up play with Ryan Taylor.
The U's pulled one back though on the stroke of half time as midfielder Simon Clist finished off the loose ball following Tom Craddock's shot that was parried by Andy Warrington.
The Millers wasted several good chances after the break to stretch their lead on what was a fairly comfortbale afternoon.
Taylor, Nicky Law and Stephen Brogan all went close while at the other end Warrington was at his best to flick debutant Paul Wotton's fierce shot from range over the crossbar.
Livewire Le Fondre almost grabbed the match ball with 3 minutes left but neither himself nor Marshall could find the net after a mad scramble in the visitors' area.