Toy snakes were waved in the direction of Eustace by Blackburn fans when he first came up against his former side at Derby’s Pride Park, just weeks after he surprisingly swapped a promotion push for the fight to avoid the drop.
He oversaw what was his first win as Rams boss in that game in early March, while this victory extends Derby’s fine run and has them up to ninth in the table ahead of Saturday’s later kick-offs.
It also has the Rams nine places and seven points above Blackburn, who had their three-game winning-run halted on the day that the club marked its 150-year anniversary.
Injuries to Scott Wharton and goalkeeper Balazs Toth late on in Rovers’ midweek win at Bristol City meant boss Valerien Ismael was forced to shuffle a backline that had given up just one goal in those three previous wins.
The Rams had an injury setback of their own to deal with soon after kick-off, as on-loan Crystal Palace midfielder David Ozoh limped off the pitch after once again being hurt in a Derby shirt.
The highly-rated 20-year-old’s first spell with the Championship club last season was hit hard by injuries, which limited him to just 10 league appearances.
The early injury proved to be the only blemish on a excellent first-half from the visitors, who again had hotshot Morris to thanks for setting them up for victory.
His towering header from an in-swinging Callum Elder corner was the game’s first effort on goal.
And with the game’s second attempt on target, it was American striker Agyemang who doubled the lead with a similarly clinical header from a deep Joe Ward cross to the back post.
It was not until Ohashi stepped up for his penalty, having been bundled over by Sanderson, that Blackburn managed their first shot on target.
Rovers were deserving of the second-half lifeline for the way they dominated the game after the break, but they failed to find a late leveller.
Tame headers from Ohashi and Andri Gudjohnsen were the only efforts that forced saved from Rams goalkeeper Jacob Widell Zetterstrom after that, despite the pressure being piled on in the final minutes.