Matej Vydra again left his mark on Nottingham Forest when he scored one and made another as Derby beat their local rivals 2-0 at Pride Park.
The Czech forward netted his ninth goal in eight games against Forest and then set up David Nugent to give Derby victory in the 100th domestic meeting between the east Midlands clubs.
Vydra and Nugent had scored against Forest at the City Ground in March and the quality of finishing once again proved decisive as the visitors squandered a number of good chances with Jason Cummings missing from close range just before Nugent's goal.
Forest had scored a stoppage-time equaliser against Derby in March but this time they conceded after only 24 seconds when Vydra was allowed to run across the face of the penalty area too easily and fire a low shot into the bottom left corner of Jordan Smith's net.
It was an awful start for the visitors but they almost hit back in the fifth minute when a cross from Eric Lichaj was glanced narrowly wide by Daryl Murphy.
Although Forest were enjoying plenty of possession, Derby looked more threatening and they were close to a second in the 22nd minute when Johnny Russell pulled the ball back from the right and Vydra drove in a shot which Lichaj did well to block.
Forest had another chance when Murphy just failed to connect with a diving header and after McKay clipped a post from 20 yards, they should have equalised in the 35th minute.
Liam Bridcutt's ball over the top sent McKay through with only Scott Carson to beat but the former England goalkeeper turned his low shot behind.
Forest had certainly created enough chances to be on level terms and they wasted another in the 50th minute when Jason Cummings scuffed a shot over from Ben Osborn's cut back.
It was a costly miss because Derby surged forward through Vydra and, as Forest stood off him, he played in Nugent who placed a low shot across Smith and inside his right post.
The finishing was the difference between the sides although McKay forced a good save out of Carson who had to stretch to tip over a 20-yard drive from the midfielder.
Smith turned over a Tom Lawrence free kick in the 63rd minute to keep Forest in the game but the Wales international was close to sealing victory four minutes later with another free kick which curled over Smith and bounced off the bar.
Lawrence had another chance to complete a highly satisfactory afternoon for Derby in the 86th minute but this time his low drive was blocked by Smith.