Ronaldo scored the only goal of the game, and his 31st of a quite remarkable season from his ninth of 11 opportunities overall in a vital 1-0 victory at rock-bottom Derby.

It was a case of persistence is a virtue from the Portuguese star as chances came and went before he finally broke the brave Rams' resistence in the 76th minute.

It was also a case of Ronaldo picking himself up after last week's FA Cup defeat to Portsmouth at Old Trafford.

The 23-year-old expressed his frustration after the Portsmouth game as he felt he was afforded little protection by the match officials.

At Pride Park, Ronaldo was bullish as he kept plugging away until he eventually grabbed the winner after earlier striking the post, whilst also seeing Roy Carroll pull off a number of fine saves.

"In the first 20 minutes we should have been four or five up, and that would have made it much, much easier for us," said Ferguson.

"You have to admire the second half from Derby. They made a real battle of it.

"But the name of the game is to win, and we have to thank Ronaldo again. It was a fantastic goal because it wasn't easy to take

"The ball bounced up off the turf and he had to get up and over it and make sure he kept it down. It was a really good finish.

"It was probably his hardest chance of the match because he had a lot of tremendous chances throughout the game."

Ferguson added: "Everybody trusts him now, and what you have to admire about the boy is that his courage is beyond question.

"I don't know how many fouls he has on him every game. Last week there were three in the first seven minutes, and seven in total, yet no-one was booked.

"So he has the courage to get up and get on with it.

"He made a comment last week that he is getting a bit frustrated with it all, but he has to trust the game.

"People want to see footballers like him, and I think we have to give him encouragement, and we do that.

"We tell him to keep doing what he is good at, not to stop. That is what we would hate to see."

As the missed chances started to stack up, with Wayne Rooney and captain Ryan Giggs guilty of missing a hatful in the first half, it appeared as if Derby would conjure a remarkable result.

But United's victory means they remain firmly on course for back-to-back titles, with Ferguson adding: "It's three points and we're pleased with that.

"We've a home game with Bolton on Wednesday, and hopefully we can win that as well.

"I think the league now is bubbling up very nicely. It should be a fantastic finish to the season."

After Wednesday's 6-1 mauling from Chelsea at Stamford Bridge, the performance on this occasion from the Rams was in stark contrast as manager Paul Jewell's side battled manfully.

But for debutant goalkeeper Ben Foster, they could even have gone into the break with the lead themselves after United had missed their glut of opportunities.

But Foster produced two superb stops to deny Mile Sterjovski and Kenny Miller to extend Derby's winless league streak to 24 games.

Jewell, though, was able to express a degree of pride at how his players had performed as he said: "There are ways to lose matches, and today we lost with a bit of dignity and went down fighting.

"On Wednesday it really was men against boys, whereas the players showed character today, although we rode our luck early on because if a goal had gone in it might have been a different story.

"But it didn't and we grew into the game, and we probably created more chances today than we have in a lot of games this season.

"It was a pleasing performance, and although we've lost again, I can accept it, and we have to take heart from it."

With regard to the imperious Ronaldo, Jewell joked: "If he was good looking, he would probably have everything!

"But he's a brilliant footballer, surrounded by brilliant footballers."