Gareth Roberts's first Derby County goal ensured former club Doncaster Rovers remain in the Championship relegation zone.
The left back doubled the Rams' advantage after Theo Robinson had given the visitors an early lead with a lob over Chris Ikeme.
Doncaster then failed to build on El-Hadji Diouf's well-taken strike.
The result ended the South Yorkshire side's five-game unbeaten run and left them four points from safety.
Nigel Clough's Derby side got off to the perfect start after Robinson chipped goalkeeper Ikeme in the 13th minute to grab his 10th goal of the season.
Ikeme, on loan at Rovers from Wolverhampton Wanderers, made it easy for the striker as he rashly raced off his line in an attempt to meet the long ball.
The keeper then pushed away a Roberts volley from a corner before the Welshman, who joined the Rams from Rovers in May 2010, found the back of the net on 55 minutes with a left-footed shot from 12 yards.
Doncaster were given a lifeline by Diouf when he controlled a flick-on cross with his chest, swivelled and slotted past Frank Fielding from six yards.
But Kyle Bennett wasted the hosts' only further chance of note when he scuffed an effort wide in injury time.