BARNSLEY-born Ipswich manager Mick McCarthy had an unhappy return to South Yorkshire on his 56th birthday as Millers strike pair Matt Derbyshire and Conor Sammon struck in either half to make it seven points from a possible nine for the hosts.
Though Ipswich went into the game in fourth place, they had won only once in their previous six outings while 20th-placed Millers had claimed four points from their last two games to lie three points clear of the drop zone.
Both sides lined up 4-4-2 and largely cancelled each other out in the first half.
But the breakthrough came in the 39th minute. Derbyshire won a free-kick off Christophe Berra out on the left, Ben Pringle swung the ball over and Craig Morgan headed back across the six-yard area where Derbyshire’s stooping header made it 1-0 to the Millers.
That’s how it stayed until the break as vaunted Ipswich front pair Daryl Murphy and David McGoldrick were kept in check.
Ipswich made a double substitution in the 52nd minute with new signing Freddie Sears replacing Jay Tabb and Teddy Bishop coming on for Paul Anderson.
Pressure built on the Millers and Adam Collin did well to tip over a flick header from Luke Chambers from a free-kick before Zeki Fryers headed off the line from Tommy Smith.
The Millers hit back and made it 2-0 in the 64th minute from the second of successive corners from Ben Pringle. Bodies went flying before the deep cross landed for Conor Newton to lay the ball into the path of former Ipswich loanee striker Sammon, on loan from Derby until the end of the season, to drive home.
Ipswich had little answer after that and substitute Jordan Bowery should have made it 3-0 in stoppage time when he raced through the middle only to be denied by Bartosz Bialkowski.