Rooney watched from the stands as he served a suspension.
He later said, “It’s difficult to put into words.
“I thought we started the game OK, we had decent control and should be 1-0 up, Michael Obafemi had a great chance.
“Beyond that, we got really sloppy, we gave the ball away a lot.
“We didn’t win tackles or do the basics right.
“In this league, if you don’t do that right, you have difficult days like today.
“It’s difficult watching it from the stands, you want to be there at the side of the pitch trying to help the team.
“Today we have to give Cardiff a lot of credit. They deserved to win the game, they were the better team.”
Rooney says he will keep emotions in check over the defeat.
He added: “I think I’ve always been quite consistent with my messages.
“Of course, you’re angry, upset and disappointed. But I think that’s more when I’m speaking to my players.
“I’m very upset with the performance because that’s not us.
“The main thing is we have to move on from this quickly.”