Manchester United players could not believe what they had seen after playing against Sporting Lisbon in a pre-season friendly in 2003.

One Sporting player had caught their eye and Sir Alex Ferguson needed to know about him.

That player was, of course, Cristiano Ronaldo.

“We were on the bus afterwards waiting for chief executive David Gill and the boss Alex Ferguson,” Rio Ferdinand told The Sun.

"We were just willing them to sign Ronaldo. Within a week he was our player.”

Ronaldo was 18 years old at the time. It was August 6, 2003 - 16 years ago today - and he ran Man United ragged.

“You see Ronaldo get the ball, and you see him turn John O'Shea inside out, and you're having a little giggle to yourself,” Ryan Giggs said in 2016, per Goal.

“He just lit up the game, all the lads were talking to him after the game and I remember we were waiting on the coach and everybody was wondering what we were waiting for.”

Meanwhile, former Man United defender Mikael Silvestre remarked, per Bleacher Report: "It was an incredible performance to watch that night.

"This kid nobody knew tore us apart for the whole game. No one could get near him; he was amazing.

"At the start, no one had even heard of Ronaldo, but by the end, everyone knew about him."

Watch Ronaldo's highlights

Check out Ronaldo’s highlights below.

Ronaldo described the evening, in which Sporting defeated Man United 3-1, as “perfect”, even being brought into the United dressing room at full-time.

“The first game that I played against Manchester United was an unbelievable game. It was the perfect night, the perfect night,” he told Sky Sports.

"After the game some of my team-mates said: 'Listen, you're going to go to Manchester, trust me!'

"Sir Alex Ferguson was there, and [they said] he wants to speak with you. I go to the dressing room, he introduced me to the players.

"For me, I was a little bit shy. And Sir Alex Ferguson said to me: 'Listen, I want you now.'

"Everything came so fast, and two days after I speak to the coach and they take me to England, and I was in Manchester, and I signed."

The rest is history.

Ronaldo went on to score 118 goals during his six years with United, winning three Premier League titles and the Champions League.