Derby picked up their first win in six Championship games thanks to three first-half goals against Portsmouth.
Craig Bryson opened the scoring for the Rams, controlling Theo Robinson's ball and netting from the edge of the box.
Chris Maguire doubled the lead from a rebound after Stephen Henderson parried Robinson's shot and Jamie Ward struck from 18 yards to make it 3-0.
Managerless Pompey had a consolation when Jason Pearce, who hit the bar at 1-0, headed home from close range.
The win lifts Derby up into the play-off places but Portsmouth, still seeking a replacement for Steve Cotterill, are now 16th.
The game was not without cost for Nigel Clough's Rams, who lost defender Mark O'Brien to injury and he was replaced by Kevin Kilbane for his 600th appearance at club level.
Pompey did have other chances apart from Pearce's headers, with Dave Kitson and David Norris heading wide from pinpoint Liam Lawrence balls.
First-team coaches Guy Whittingham and Stuart Gray have been taking charge of the visitors, who say they are hopeful of appointing a new manager soon.