But Juan Mata’s free-kick levelled the scores before Alex Sandro’s own goal gave the Red Devils an unlikely 2-1 win.
And Ronaldo insists that Juve deserved all three points after missing several good chances to put the game to bed.
“I was happy with the goal but we are disappointed because we should win the game easily, by three or four goals,” he told Viasport.
“Manchester didn’t do much, they created two chances from set pieces. English teams are always looking for set pieces.
“But we will learn from our mistakes and we are still top of the group and we are good.”
In truth, Juventus could have had the game wrapped up before then with Sami Khedira and Paulo Dybala hitting the woodwork.
“The Champions League is a special competition, where you could be winning, but can’t relax, as anything can happen,” Ronaldo added.
We dominated the game for 90 minutes, had so many chances, could’ve killed it off three or four times, but we relaxed and were punished.
“Manchester United did nothing to win the game. You can’t even talk about luck, because you have to find your own luck and in this case we just gifted it to them.
Ronaldo has won the Champions League in the last three seasons at Real Madrid but believes it is far too soon to be touting potential winners.
“It is too early. We have to take it step by step,” he said when asked if Juventus were contenders.
United boss Jose Mourinho insisted he has happy with the performance of his players throughout the game.
“The game was a very good game. It was top,” he said.