Best's strike on the stroke of half-time dents Town's Play-Off hopes
The former Southampton striker bundled the ball over the line just before the break after Matt Derbyshire had escaped down the right.
Ben Pringle was inches away from finding the net against his former club in added on time but the ball slipped wide and Town slipped four points off the top six.
Town stayed with the same side that beat Blackburn in midweek, with new loan signing Liam Feeney starting on the bench.
Freddie Sears sent a header over the bar in the game’s first opening, Bart Bialkowski then off his line to clear from Derbyshire.
Sears couldn’t generate much power with a left foot effort after he found space inside the Rotherham box from Brett Pitman’s pass.
Jonas Knudsen tested the Millers’ rearguard with a surging run into the box, his cross forced behind for a corner. Then Rotherham broke from the flagkick and it needed Jonathan Douglas to prevent Derbyshire getting in.
Bialkowski saved from Richard Smallwood in an even opening 20 minutes, Lee Frecklington’s shot blocked on the edge of the Town box.
Luke Hyam linked up with Daryl Murphy to create a yard of space for Sears but his cross cannoned to safety.
Greg Halford’s long throws were a source of attack for the visitors and Frecklington lobbed just over the bar when the ball broke to him, then Grant Ward fired wide.
Luke Chambers tested Camp with a strike on the turn, Bialkowski then pushing Ward’s shot away from danger before the Millers got the breakthrough just before half-time, Best forcing the ball over the line from Derbyshire’s cross.
Feeney replaced Douglas at the break and Town started the second-half in positive fashion, Sears having a shot cleared off the line, Chambers’ header saved by Camp, then Pitman going close.
Feeney’s willingness to take on the Rotherham defence lifted the Blue Army and from another cross from the Bolton loanee, Murphy was inches away from directing his header on goal.
Knudsen headed at Camp from Feeney’s cross as Town pressed for an equaliser, Sears sending a right foot curler wide of the far post.
Sears and Pitman linked up on the edge of the box, Pitman judged to have been fouled by Lloyd Doyley, the former Bournemouth striker smashing the free-kick high and wide.
Pringle replaced Pitman for the last 20 minutes, the midfielder sending a 25 free-kick into the box but Camp held firm.
Kevin Bru replaced Hyam, Derbyshire making way for Joe Newell, Best for Jonson Clarke-Harris in a flurry of changes for the closing stages.
Ward could have wrapped the points up for Rotherham three minutes from time but he slashed his shot wide of the far post from Halford’s pass and there was just time for
Pringle to goes agonisingly close to grabbing a last minute equaliser, his shot a yard wide.