Tyrhys Dolan scored from close range after Ben Brereton hit the post in the 11th minute and former County midfielder Bradley Johnson smashed in a second from 25 yards a minute later.

Marshall could do nothing about Johnson's second in the 15th minute when another fierce strike was deflected past him but he did well to deny Brereton and Adam Armstrong before the break.

Derby were better in the second half and created chances but Blackburn scored again in the 77th minute when Harry Chapman broke clear on the right and set up Armstrong for a simple finish.

Cocu was scathing about the way his team performed out of possession.

"Last season we had two bad games and I compare this a little bit with those games because I think today a big part of our defeat was our attitude, our passion, willingness and desire to defend and track down," he said.

"You can talk about tactics but in any system it's about how you execute it and if you concede three goals in four minutes, I think that says enough.

"We showed some good football but I am worried about how we present ourselves when we don't have the ball and that's a big part of the game.

"We had 65 per cent possession, so what do we do when they have the ball? It's not good enough, that's underperforming.

"We always say stay in the game, for a few minutes get yourself together, take initiative and go forward again but by conceding three goals and two similar goals, it's unacceptable.

"In the second half, the attitude was much better but it's a little bit late when you are 3-0 down and that's what I'm upset about because I expected we would have learnt from those games of last season."

Rovers took their goals tally for the season to 11 in three games.

Blackburn manager Tony Mowbray said: "The players deserve huge credit for their work-rate, their effort and energy they are putting into the games and are getting the rewards for all the hard work we've done over the last six months when we've tried to change the team around a bit.

"I think the benefits are there for all to see. I'm told we had 23 shots so to score four, I think it's been one of our issues, the percentages. We've worked a lot on finishing and the final pass into the box and picking the right pass when we get into crucial areas.

"That was something that was letting us down, we were able to dominate games but not finishing teams off because we weren't taking chances but I don't think you can be too greedy.

"For Johnson to score, that's fantastic for him. He's growing into this football club a little bit now, he looks as if he's irreplaceable at the moment, in the last four games anyway, so let's see if we can maintain it and Bradley can maintain it."