Adam Hammill missed an early penalty in a goalless first half then Adam Davies conceded a spot kick which he saved but the rebound was tapped in by Jamie Proctor who then completed a hat trick with two superb strikes. Kieffer Moore finished off a miserable afternoon for Paul Heckingbottom who played a full strength team.
In front of more than 1,500 Reds fans, Ike Ugbo brilliantly won a penalty early on after dispossessing a defender on the left wing, skipping past another and then being brought down in the box. Hammill's spot kick was excellently tipped onto the left post by home goalkeeper Richard O'Donnell.
Rotherham had the better of the rest of the first half with Adam Davies saving from Jamie Proctor and former Reds trialist David Ball.
Barnsley were dealt a blow when Lloyd Isgrove limped off injured but his replacement Joe Williams almost claimed an assist when, after a fine run, he played through Tom Bradshaw who was denied by a good one on one save from O'Donnell.
Tom Bradshaw should have levelled immediately but fired over the bar from three yards out with an open goal after meeting a low cross from halftime substitute Jason McCarthy. Instead it was Rotherham who doubled their lead when Williams played a good ball over the visiting defence for Proctor to smash in a fine volley from the right of the box.
Davies kept the score down with another fine save from another Vaulks long ranger and, at the other end, substitute Stefan Payne won a tackle to go clear through but was denied by an excellent save.
