England's top scorer in 2012, Welbeck had found the net just once for United this season.
But that did not stop the 22-year-old getting the better of Sergio Ramos in the first half, powering home the header that set United up for an encouraging 1-1 draw.
It was the high point of an excellent all-round display from Welbeck, who seemed to have fallen so far down the pecking order at United he was linked with a loan move to Reading before the transfer window opened.
There was never any chance of that deal taking place.
And Ferguson could not have been more delighted with the striker's contribution.
"He was marvellous," said Ferguson. "It is a pity he got cramp at the end of game, but he worked so hard. It was only his second goal of season. We expected more, but he is young.
"They found it difficult to handle him."
It was also a night to remember for goalkeeper David de Gea, who has found himself under so much scrutiny recently, with former United full-back Gary Neville among those to criticise the Spain Olympic keeper for Tottenham's equaliser in last month's draw at White Hart Lane.
"De Gea was excellent," Ferguson said. "He made three or four top saves. He has been improving all season."
"There was one save, I think it was in the first half when he got a touch of the ball that put it on the outside of the post. It was an absolutely superb save.
"It's a difficult place to come back to and to perform like that. He played for Atletico, so he'll be pleased with that."
Team-mate Ryan Giggs added: "It's good for him to come back to Madrid and put in such a good performance. He is a top keeper and his shot stopping is second to none.
"He is maturing all the time and he has showed that tonight. He has come to Madrid with a lot of pressure on him, being from Atletico, and he has produced the goods."
Looking ahead to the return leg at Old Trafford on March 5, Ferguson added:
"We made chances all the time, and hopefully we don't regret that," he said.
"The away goal is important but it's not finished, of course, because Real Madrid are a fantastic counter-attacking team. It gives us a good chance. I look forward to it."