Wigan striker Nathan Ellington snapped up his third goal in as many games and flashed a warning to the first division.
The £1million man, whose 22 goals last season helped Wigan into the division for the first time ever, sparkled as the surprise high flyers dumped Ronnie Moore's Millmoor outfit.
The former Bristol Rovers man came on as substitute at Burnley and scored the winner before coming off against Ipswich.
And when he grabbed Wigan's second at Rotherham it put Paul Jewell's side in the comfort zone.
The win was no more than Wigan deserved after they produced graft and craft that had the Millers in knots.
Rotherham went close early on when Scott Minto whipped in a cross from the left after three minutes and Richie Barker's power header was just over the top.
A weaving run from Chris Sedgwick carried the Rotherham winger into the area but keeper John Filan dropped smartly to his left to cut out the angled shot.
Andy Monkhouse pounced on a loose ball to open up the Wigan defence but his volley went wide.
Wigan, oozing with confidence after their two impressive wins over Burnley and Ipswich, went close when Ellington caused problems for the home side.
His best opportunity came after 19 minutes when a quick throw-in had Rotherham back-pedalling. Ellington spun cleverly and lashed in a spectacular volley but his shot drifted over the bar.
And when Neil Roberts found a way through the Rotherham defence, keeper Mike Pollitt tidied up cleverly.
The breakthrough came eight minutes into the second half when Ellington eased a deft ball through for Jason Jarrett who lashed in his first league goal for the club.
Six minutes later Ellington snapped up the second, volleying in from the edge of the area after Neil Roberts chested down Andy Liddell's cross.
Roberts added the third driving in a low shot when Guy Branston's sliced clearance fell for him.