Rovers by contrast have now won five of their last six games and are two points outside the top six.

Tony Mowbray named an unchanged side from the win at Stoke, while Phillip Cocu made two changes for the Rams, including a return from injury for Krystian Bielik.

In-form Bradley Dack almost profited from a poor clearance early on, showing composure to fashion an opening but he directed his shot inches wide from a tight angle.

On the half-hour, Dack had a chance to finish off a flowing Rovers counter-attack but swept his shot over the bar on the edge of the area, and Danny Graham went close towards the end of the half, glancing a header into the side netting.

Rovers should have taken the lead on the stroke of half-time when Bielik was caught dithering on the ball and Lewis Travis released Armstrong in the area but his shot was repelled by the foot of Ben Hamer when he ought to have done better.

The Rams were hardly in the game but almost took the lead 10 minutes after the break through a sensational 30-yard shot from Bielik which curled just wide with Christian Walton well beaten.

But they were behind in the 57th minute when an incisive Corry Evans pass found Armstrong on the edge of the area and he hammered a thunderous drive that flew past Hamer at the near post for his fourth of the season.

Ryan Nyambe put his body on the line to block a rasping Kieran Dowell drive, before Blackburn substitute Sam Gallagher saw a shot of his own blocked.

The Blackburn substitute almost put a second on a plate for Armstrong, but his deflected shot looped just over.

Derby pushed for a late leveller and finally forced Walton into a save when substitute Jack Marriott turned sharply and unleashed a rasping effort 12 yards out, but the Blackburn stopper got down well and ensured the points went to Mowbray's men.