Cristiano Ronaldo will never forget the day he introduced himself to the world.

The Portuguese superstar wore boots with “06.08.03” stitched into the lining when he returned to Sporting Lisbon in last season’s Champions League, to remember the date of that friendly against Manchester United 14 years ago.

Ronaldo was 18-years-old when he tormented the Red Devils in front of Sir Alex Ferguson, Rio Ferdinand and Roy Keane.

After watching the skinny winger display a confidence that belied his age, Ferguson realised that he couldn’t return from Portugal without the player.

Man United would end up paying £12.24 million for Ronaldo, and you know the rest.

'He was there to put on a show'

Former United defender Danny Pugh was fortunate enough to get front row seats to the Ronaldo show.

He was named on the bench, alongside Keane, Ryan Giggs and Ruud van Nistelrooy, and has revealed just how impressive Ronaldo was in an interview with Bleacher Report.

“The first time he picked up the ball, he did a bit of skill, beat a player and all of us on the bench sat up together and took notice," Pugh said.

"He was there to put on a show. Every time he got the ball, he wanted to do something, he had so much belief.

“He was still quite slight then, but he had so much natural talent. It was the way he carried the ball and skipped past players."

Ferguson warned his players about Ronaldo before KO

Yet Ronaldo’s outstanding performance shouldn’t have surprised Man United’s players.

After all, they were warned about the player who would go on to win four Ballon d’Or awards and break numerous goalscoring records.

Ferguson was concluding his pre-match speech when he remembered one more thing: Ronaldo.

Former United defender Mark Lynch recalls what the Scot told his players, per Bleacher Report: “Oh, lads, and one final thing: They have a talented young winger. Look out for him, OK? He's strong and agile. He's quite good.”

‘Quite good’. That’s some understatement.

"That was it," Lynch, who would come on in the second half, added. "No big warning, no time spent on him, just a few words, almost as if Sir Alex wanted to shock us."

Ferguson’s players quickly realised what he was on about. Nobody could get close to him, with John O’Shea enduring a game from hell.

The 32-year-old has gone on to achieve extraordinary things in the game, but nobody will ever forget how his story began.

What is Cristiano Ronaldo's greatest ever moment? Let us know in the comments section below!