At the Kassam Stadim, Steve Evans' Millers smashed four goals in 14 minutes as they stretched their unbeaten run to six matches.
David Noble put Rotherham ahead after half an hour, Kari Arnason headed in Ben Pringle's corner three minutes later and skipper Johnny Mullins made it three with a 16-yard strike.
Pringle added a fourth before half-time with a far-post tap-in.
Paul Benson's last-gasp header earned Cheltenham a 1-0 home win over Chesterfield. The striker - who is on loan from Swindon - met Billy Jones' cross one minute into added time to move the Robins back into the top three.
Port Vale remain in second but continued to suffer from promotion jitters as they were held to a goalless draw at home to Bradford. Vale's night was also marred by a late red card for Doug Loft.