When this Wimbledon began, the only teenagers you would have expected to feature on Centre Court in the second week would have been the ones fetching Rafa Nadal's towel.
So you want to see a teenage tennis player in command at the All England Club, lashing the ball, and playing with a nerveless ease? You're going to have to pull a Boris Becker film from the video archives.
But that was a week or so ago, and this is now, and tennis is different now. The Nick Kyrgios story had built and built during his first three appearances; it exploded during a fourth-round match against Nadal, the world number one, a former Wimbledon champion, a winner of 14 grand slam titles, and one of the greatest players in tennis history. "Absolutely stunning," said the watching John McEnroe.
Tuesday was a wild day on Centre Court, with Nadal beaten by a fearless 19-year-old Australian ranked outside the world's top 100, and someone who earlier this summer lost in the first round of a small, Challenger-level tournament in Nottingham.
Let loose on the lawns and on the tennis elite by an All England Club committee who gave him a wild card, Kyrgios was bouncing and bouncing around Centre Court, he was hitting 130mph serves and he was taking giant swings with his forehand. And, with one through-the-legs 'tweener' winner, he landed what must be the cheekiest shot ever played on this grass. This was a wicked combination of power, poise and the insouciance of youth. And it was too much, over four sets, for the current French Open champion.
Anyone who imagined that Kyrgios would be unsettled by making his first appearance on Centre Court is possibly still sitting in the stadium, waiting for the Australian's nerves to kick in. His own mother was among those who considered her son beating Nadal to be an impossibility. As Kyrgios said on stepping off court: "I saw in an interview that my mum said that he was too good, and that made me angry."
As their mothers, and everyone else, is aware, teenage tennis players simply aren't supposed to do this. Not on this stage. Not to Nadal. As the rankings stand now, there are no teenagers in the men's top 100 (Kyrgios will jump into double digits when that list is updated on Monday morning).
Men's tennis has never been as old as it is now - with every season that passes, it seems that the average age of players at the top level moves closer to 30 - and the result has been that teenagers have been pushed to the margins. The received wisdom on teenagers had been they would have to wait to mature - physically, mentally, emotionally - before being ready to make an impact on the tennis stratosphere.
Nadal, the champion here in 2008 and 2010, had shown some vulnerability in his first three rounds this summer. On all three of those occasions, he lost the first set before coming back to win in four. For the fourth match in succession, he went a set down, yet this time Nadal couldn't make his way back. That had much to do with the might of his opponent's serve. In all, Kyrgios struck 37 aces.
And this wasn't even the first extraordinary act of the Australian's tournament; that came in the second round when he saved nine match points when turning around a two-set deficit against France's Richard Gasquet, a former semi-finalist here. In a parallel universe, Gasquet converted one of those match points. But, in this one, Nadal is out of the tournament, and Kyrgios is through to the last eight, with his quarter-final against Canada's Milos Raonic to be played on Wednesday.
It had been thought that teenage talent disappeared from view on the day Nadal turned 20. The last time a 19-year-old had this much impact on the slams, beating a world number one, was when Nadal overcame Roger Federer in the semi-finals of the 2005 French Open - and the Majorcan went on to win that tournament. Kyrgios is still a long way from winning this title. But this was one hell of a performance, and who would be surprised if he wins Wimbledon at some point in his career? "You're asking who are the next big things in men's tennis? You're looking at one of them," McEnroe said.
Mark Hodgkinson is the author of Lendl: The Man Who Made Lendl. He is writing daily pieces for ESPN during Wimbledon.