Nathaniel Mendez-Laing inspired Derby to a 2-0 victory and sent Exeter sliding to a sixth straight league defeat.
The winger was a constant threat and scored the opening goal before Conor Washington secured the Rams’ second home league win of the season late on.
Derby pushed Exeter back from the first whistle but despite getting dangerous crosses into the box, could not put the ball away.
Exeter were starting to come into the game when Derby finally finished a slick three-man move, with Mendez-Laing firing home Max Bird’s pass from 12 yards in the 30th minute.
Derby should have had more to show for a dominant first-half display and although Exeter had hardly threatened, they needed a second goal.
Martyn Waghorn and Louie Sibley had shots blocked before Mendez-Laing was flagged offside when he headed in at the back post.
But Derby made the game safe in the 79th minute when Washington cut in from the left and drove a low shot inside the near post.
