Alongside Ferdinand, Jonny Evans was an able assistant in repelling Real attacks. Michael Carrick and particularly the dynamic Phil Jones shielded the back four well. Jones remains raw at times but the rich potential, the energy and hunger to win the ball back, bodes well for United and England. Rafael recovered from his first-half mauling by Ronaldo and Özil to enjoy a steadier second half. Before cramp took control of his legs, Danny Welbeck was outstanding, scoring with a fine header and striving hard to ensure Ferguson’s tactical game-plan paid off.

But it was a slight-framed Spaniard who took the headlines. It would be tempting to suggest that a keeper born in Madrid came of age here on Wednesday night. De Gea is only 22, still developing and will make mistakes in the future, particularly when placed under pressure at corners in the Premier League, yet this was undoubtedly a significant moment for him.

At a time when there is plenty of talk about United looking to recruit Asmir Begovic from Stoke City, De Gea picked the right moment to remind his critics of his qualities. Early on, he had to endure the barracking of the Ultras Sur, inevitably as a former Atlético player but he ignored them, focusing on frustrating their players. No blame can be directed at De Gea over Ronaldo’s goal, a header that carried echoes of his goal in the 2008 quarter-final in Rome.

Some of De Gea’s saves were routine, some were inspired while others would not have been found in any goalkeeping manual. He denied Fábio Coentrão early on, stretching out his fingers to steer the shot against a post. He kept out three efforts from Di María, one from Ronaldo, two more from Coentrão, including one extraordinary stop with his feet, prompting the thought that he was a defender with gloves. He also frustrated Gonzalo Higuaín and Sami Khedira. “He has been improving all season,’’ said a delighted Ferguson. “There was one save in the first half which he touched on to the post, a superb save. I’m pleased for him, an Atlético boy playing here in Madrid, but he has done well.’’ He needs to do well again, and again and again, gaining the consistency that sets the great keepers like Gianluigi Buffon apart.

He needs to do well in the second leg on March 5. Real will counter-attack, hunting goals through Ronaldo again and the Portuguese would love to score on his return to a place where he spent six productive years. The respect between Ronaldo and United was reflected by the way he kept his goal celebrations to a minimum, by the way Ferguson waited by the tunnel to embrace him at the end, by the way Ronaldo went into the away dressing room to see old friends.

Real will need a huge performance from Ronaldo at Old Trafford. It is the game which could decide Mourinho’s future here. Going out of the Champions League in the Round of 16, and trailing Barcelona in La Liga, is not a fate Real’s powerbrokers will accept demurely.

He was constantly out of his seat, never able to relax. When United fans began chanting “sit down Mourinho”, he responded with a regal wave. Mourinho’s radical fashion statement of snood and suit was rather like some of Real’s defending at corners: it did not quite work.

After 19 minutes, Wayne Rooney curled over a corner and Welbeck timed his little run and leap well, exploiting Sergio Ramos’ lax marking to score with a firm header. Di María had appeared to be guarding that post but was drawn across as Rooney’s corner came in, gifting Welbeck the space. Welbeck, a boyhood United fan, ran to the corner and saluted the away contingent celebrating up in the Gods.

A rather more established name than took centre-stage. Ronaldo was fouled by Jones, allowing him a free-kick opportunity 30 yards out.

His kick flew into the wall, and his left-footed follow-up went wide.

Just before the half-hour, Ronaldo equalised. Di María’s delivery was excellent, the ball lifted across towards Ronaldo, who jumped higher than Patrice Evra to score with a powerful header.

Both sides kept going for it. Rooney and Xabi Alonso went in hard but fairly on each other. A quick touch of the hands confirmed their respect. Old troubles resurfaced. Rafael panicked and pulled down Özil, earning a booking from Felix Brych.

On the hour, De Gea made an astonishing save, albeit unconventional keeping out Coentra’s effort with his feet when it seemed easier to use his hands.

United were now coming under sustained attack but Ferdinand was superb. They almost scored a second away goal. Van Persie’s shot was pushed on to the bar by Diego Lopez. Van Persie then had a golden opportunity to score but scuffed his shot. Ryan Giggs, whose arrival was greeted with respectful applause by the Real fans, then squandered a chance, strangely deciding not to shoot first time, even though the ball was sitting up nicely for his left foot. He took an extra touch and Real slammed the door.

Ronaldo then sent a dipping 40-yard free-kick just over but United could have won it but Lopez saved from Van Persie. Brych, strangely, did not allow United the time to take the corner even though there were a few seconds remaining. United voiced their frustrations but departed satisfied. De Gea ensured that.