The 18-year-old unleashed a 25-yard shot into the top right corner and Derby dominated the rest of the first half with Chris Martin doubling their advantage in the 41st minute after Christian Walton could only parry a Graeme Shinnie shot.

Martyn Waghorn hit the inside of a post three minutes later and although Rovers improved they lacked a cutting edge.

Ben Hamer saved a deflected shot from Amari'i Bell but Martin sealed the victory with an 85th-minute penalty after Jason Knight was bundled over and Rovers had John Buckley red-carded for a late lunge on Curtis Davies.

The win takes Derby to within five points of the top six and Cocu is optimistic Rooney will soon be back.

"He has a small muscle problem which will be assessed tomorrow to find out exactly what it is but we don't expect it to be a big issue and maybe he is available for the next game," said Cocu.

"He couldn't train on Saturday, he tried but it was not good enough and we didn't want to take the risk of him pulling a muscle and is out for the season. Tomorrow he will have a scan and then we will know a little bit more.

"Wayne was part of the team before in the preparation for the match, and at half-time and after the game he joined in with everybody. He observed from on high so he could see some tactical details so he was involved with the team."

Sibley followed his eye-catching performance against Manchester United last week with another impressive display and Cocu said: "It's not bad if you start your career with such a goal!"

Blackburn manager Tony Mowbray bemoaned his side's missed opportunities.

He said: "We missed some good opportunities, goals change games and we didn't take the chances when they came and paid.

"We are disappointed, we came here with an ambition to get in the top six and believed that we could but Derby played well.

"We've got nine games to go, we've got a lot of teams to play that are around us so let's see where we go. We believe we can beat anybody at home and in spells today we showed we can be a threat away as well."