The Portuguese superstar did not enjoy the most productive of afternoons at Pride Park but still came up trumps towards the game's death as he found a winner.
It took until the 76th minute to find a breakthrough against the basement dwellers, as Ronaldo and his team-mates were guilty of squandering numerous opportunities.
The post denied Ronaldo on one occasion, and the superb Roy Carroll on others, but Earnshaw believes it is a measure of the man that he persevered before eventually prospering.
"The game was a real battle between Roy and Ronaldo, and Roy was winning it until the goal," said Earnshaw.
"You cannot help but admire him. At least you do until you play against him - and then you don't give him any respect and hope he has a bad day.
"You have to make it as hard as possible, but we're talking about one of the top three players in the world.
"You look at these last two seasons, and he has almost been toying with the Premier League. That's how good he has been. He has been toying with everyone.
"Against us he missed a few chances. But he still managed to get the goal, and that's him.
"United create so many chances, and that's why he and they score so many goals.
"If they miss one, two, three chances, they know a fourth and a fifth will come - and so on. That's the difference."