Ronaldo, starting his first home match in over two months due to his ankle injury, also created a goal and missed a penalty as Madrid made hard work of seeing off lowly Almeria.
The former Manchester United man was booked for taking his shirt off to celebrate scoring and that proved costly as four minutes later he was handed his marching orders after picking up a second yellow following a tussle with Michel.
Ronaldo said: "Removing the shirt was an instinctive reaction. I know that I messed up, but I'm human. I did not mean to. These things happen in football and hopefully I'll learn. I apologize to myself and my teammates."
And he admitted he deserved his dismissal: "I am not a liar. I hit him. I've asked forgiveness."
On missing the spotkick, he added: "It made me angry. I missed the penalty. I was angry. I do not like losing and I hate failing. I am a professional.
"But I did not give up and I felt happy for the goal from Karim (Benzema) and mine."