Joe Partington fired high over the Rotherham bar after six minutes, but Bournemouth's game plan went out of the window in the 18th minute when Rotherham took the lead.
A ball in from the left was headed out by the visitors but only straight to Mark Hudson on the edge of the 18-yard box and he struck a sweet left-foot volley past on-loan goalkeeper David Button.
And Rotherham should have had a second minutes later when Button fumbled a high cross and dropped the ball, but Mickey Cummins fired the lose ball over the bar.
Hudson fired over from Reuben Reid's lay off and new signing Jason Taylor fired over the bar following a Jamie Green corner as Rotherham continued to press forward.
In first half injury time, Button pulled off a magnificent save to keep out a Nick Fenton header following a left-wing corner.
Bournemouth brought on two substitutes at the break pushing more men forward and Joel Ward was quickly in action with his close-range header bringing a good save from David Stockdale in the Rotherham goal.
But Bournemouth's cause was not helped after 63 minutes when Danny Hollands received his marching orders after collecting two yellow cards in the space of just three minutes.