The home side started strongly when Richard Brindley’s low effort gave them the lead in the 10th minute, but Shaun MacDonald equalised on the stroke of half-time.
After the break, things quickly went downhill for the Millers as Bournemouth proceeded to launch a brutal attack and goals from Junior Stanislas and Ryan Fraser took them into a clear lead before a further two superb goals from Yann Kermorgant sealed the win.
Rotherham were forced into three changes for the game with Emmanuel Ledesma and Tom Lawrence recalled by parent clubs and Scott Wootton not given permission to play – and although they took the lead, they were emphatically beaten by the Championship pace-setters.
Veteran full-back Ian Harte almost gave the visitors a ninth-minute lead when he whipped a free-kick off the underside of the bar.
The away side felt the shot had crossed the line and were then caught on the break a minute later when full-back Brindley, only recently recalled from a loan spell at Scunthorpe, fired in a shot from the edge of the box that beat Lee Camp into the bottom corner.
Stanislas mis-hit a shot wide before Jordan Bowery shot into the side-netting from the edge of the box at the other end.
Bournemouth had started to improve their passing play and it paid off a minute before the break when MacDonald slid the leveller past goalkeeper Adam Collin after being played in by Kermorgant following a long spell of possession.
The visitors’ dominance continued throughout the second half and Adam Smith tested Collin from the edge of the box with a swerving right footed effort that had to be tipped wide for a corner.
Eddie Howe’s men took the lead in the 57th minute when Stanislas made amends for his earlier miss, rounding Collin before tapping into the empty net from Dan Gosling’s pass.
Fraser made it 3-1 in the 64th minute when Rotherham were again carved open by a slick passing move. Kermorgant put Fraser in on goal with a smart touch and he finished coolly beyond Collin into the bottom corner.
Kermorgant then tucked in an easy chance after latching onto a cross from Stanislas’ centre midway through the second half, with Rotherham defenders again caught admiring the attacking play.
The Frenchman doubled his tally on 72 minutes after tapping in following Collin’s wonderful save from Steve Cook’s powerful header, before substitute Matt Derbyshire missed two late chances for Rotherham.