Lyon almost levelled the tie at 2-2 in the second half when Kader Keita fired a shot against the post.
His goal was well-taken - it may not be the best goal he has scored this season but it may turn out to be one of the most important
Sir Alex Ferguson on Ronaldo
But Ferguson felt his side were solid at the back despite their lack of fluency at the other end.
He explained: "Some nervousness came in, because we didn't take the chances and kill the game - so we were on a knife edge.
"The more important part of it was that we were defending well. The back four were quick to advance on to their opponents, and that made a big difference.
"Apart from the shot from Keita that hit the post, they didn't really make a chance."
And Ferguson was quick to pay tribute to Ronaldo, who has now hit 30 goals in his last 30 games.
"His goal was well-taken," Ferguson added. "It may not be the best goal he has scored this season but it may turn out to be one of the most important.
"He has scored 30 goals already this season, and it is only the start of March. Potentially there are 16 or 17 games ahead of him, so he could end up with an even higher score.
"For a wide player to do that is fantastic. It is a great contribution."
And United were also able to celebrate equalling Juventus' Champions League record of 10 straight home wins.
"It is a marvellous record," said Ferguson. "The supporters have a lot to do with that. They were fantastic again here."
Lyon coach Alain Perrin felt his side did not deserve to progress: "You cannot argue with the fact that Manchester United deserved to go through over the two legs, even if our effort perhaps deserved more than we got.
"I think the late goal in the first leg influenced this match."
Bookmark with:
What are these?