Andreas Weimann came back to haunt his former club with the opening goal that set Derby on their way to a 2-0 win over Aston Villa at Pride Park.
The Austria international, who joined County from Villa in 2015, scored after a mistake by Glenn Whelan and Villa created little before Johnny Russell secured Derby's fifth victory in six games.
Villa's injury problems were highlighted by Josh Onomah playing as a striker but it was their defence that came under pressure from the start as Matej Vydra cut them open.
Only 32 seconds had gone when the Czech attacker played in David Nugent who looked certain to score until a great challenge by Neil Taylor put the ball behind for a corner.
Derby were quicker to the ball but Villa broke quickly in the sixth minute with Jack Grealish finding Onomah on the edge of the area but he was quickly closed down.
Villa had another scare in the 15th minute when a cross from Craig Forsyth caught Sam Johnstone in two minds but he recovered to push over Nugent's header.
The visitors appeared to have settled but in the 24th minute, a dreadful ball from Whelan put Vydra clear and his pass was turned in at the back post by Weimann.
Derby almost got in on the break but Vydra's ball lacked accuracy and although Conor Hourihane had Villa's first effort on target in stoppage time, it had been a poor first half for the visitors.
They started the second with more urgency and almost equalised soon after the restart when Albert Adomah's cross was flicked on by Onomah and Robert Snodgrass saw his shot blocked on the line by Richard Keogh.
The Republic of Ireland defender was involved at the other end on the hour when his firm header from a free-kick was held by Johnstone who had to dash out of his goal to clear as Derby threatened again.
Johnstone again showed quick reactions in the 68th minute when he just beat Vydra to a loose pass from Mile Jedinak and he turned over a Bradley Johnson header two minutes later.
Villa were giving the ball away too often and Onomah's wild shot from outside the box in the 76th minute summed up their growing frustration, although Grealish remained a threat.
Scott Hogan glanced a header wide as Villa finally started to press in the closing stages but Derby defended strongly and the home side sealed victory in the first minute of added time when Keogh sent Russell clear to slide the ball under Johnstone.
Russell was denied a second by Johnstone but Derby had done more than enough to beat a Villa side who had been second best by some distance.