Cardiff handed Wayne Rooney the biggest defeat of his short managerial career as Leandro Bacuna scored twice, with Wales pair Kieffer Moore and Will Vaulks also on target.

The win took Cardiff to sixth and McCarthy – who arrived in January with the Bluebirds 15th having lost six successive games – has now won seven and drawn three during his time in the Welsh capital.

"If you lose it's all doom and gloom and sack the manager," Cardiff boss McCarthy said.

"Now we're flying and we're in the play-offs, we're getting promoted. You won't get me carried away with it.

"It's a lovely time when you're winning football matches, but you've got to win the next one.

"There's no point getting carried away and having your head in the clouds.

"Everybody gives you a pat on the back but suddenly there's a knife in their hand. I don't get carried away by that stuff. There's a lot of good teams in this league and we'll just keep pecking away."

Cardiff's night was soured by what appears to be a serious knee injury for defender Joe Bennett.

The left-back was moving towards the ball but unchallenged as he collapsed to the turf, and lay motionless for six minutes before medics took him away on a stretcher.

"He's not good," McCarthy said. "I'm not a doctor or a surgeon but he'll be assessed tomorrow.

"It's exceptionally tough for him, you could tell it wasn't right. There will be suspicions of being ligaments and ACL, all that.

"Until he has a scan and the doctors have decided what it is I'm not going to try and attempt to say what it is.

"Everybody will have a guess. When someone goes down and doesn't move you know he's hurt and it's a real sore one."

Derby had won six of their previous nine games, with Rooney engineering a recovery in the Rams' battle against relegation since his November appointment.

But Rooney paid the price for resting several regulars, saying: "We have been monitoring the players over the last few weeks because we've had a lot of games and players needed a rest.

"I felt it was the right time to give them that rest. It was a gamble, I know that, and it was a gamble that didn't pay off.

"It was an opportunity for players to come in and show me if they deserved to be in the team.

"It's not nice to concede goals and it's something I'll be speaking to the players about. But I don't go over the top when we win a game and I'm not going to worry that much about losing this game."