Professor Rafa schools young Thiem

— -- PARIS -- Among the many charms of this sport are those auspicious moments when the future collides violently with the present, when the next generation emphatically announces itself to the reigning establishment.

On the same day Serena and Venus Williams departed from Roland Garros in the second round, an 18-year-old from Chicago -- the youngest player in either main draw -- managed to beat the highest-ranked Frenchwoman on her home court. Whether Taylor Townsend is destined to win Grand Slam singles titles remains to be seen, but the juxtaposition was inescapable.

And so it was that Rafael Nadal, the No. 1-ranked player in the world, met the 20-year-old Austrian Dominic Thiem on Thursday. Historically, Nadal has taken a dim view of generation next. He has never, ever lost to a player born in the 1990s, posting a spotless 20-0 record.

Make that 21-0. The future, apparently, has not arrived quite yet.

At times, Thiem showed some sparkling chops -- and a sweet, swinging one-handed backhand -- but he just didn't have the mental or physical stamina to hang with the man who is looking for his unprecedented fifth consecutive French Open title and ninth overall. The final score was 6-2, 6-2, 6-3, but the kid acquitted himself well.

Thiem, who said he made a lot of "rookie mistakes," did not have any illusions going into the match.

"Yeah," he said, "I expected it, everything that came after. He lost one match here in 10 years or something, so I knew that it's going to be the biggest challenge in my tennis career."

Thiem (pronounced "teem") sometimes swung for the fences; he had 41 unforced errors, 22 more than Nadal. And like a typical 20-year-old, he was underserved; Nadal broke him no fewer than seven times.

Nadal, at his postmatch news conference, called Thiem a "dangerous" player and said he didn't appear afraid of the moment.

"I didn't have that serve at the age of 17," he said, referring to his first visit to the grand stage. "I didn't have the backhand, I didn't have that power. So always is question of keep improving, make the normal evolution, be enough humble to keep practicing as hard as you did before.

"I have almost 28 [years]. [Novak] Djokovic and Andy [Murray] has 27. [Roger] Federer has, I don't know, 32. The new generation, new players, have to come. We're not going to be here for 10 more years."

In 2011, Thiem reached the junior final here as a 17-year-old and won the prestigious Orange Bowl.

At 20, he is the youngest player in the ATP World Tour's top 100. He is more than two years younger than Milos Raonic and Grigor Dimitrov, who are viewed as the best of the incoming group.

"He's got a huge upside," said Brad Gilbert, who coached Agassi and Murray. "He's 6-foot-2, 180 pounds and it looks he hasn't even filled out yet. The big guys -- Nadal, Federer, Djokovic and Murray -- they've wiped out two generations of players from winning Slams. Three years from now, when the opportunity comes, he'll be competing to win these things."

Thiem successfully qualified his way into ATP draws seven of eight times, including the Australian Open and more recently Madrid -- where he beat world No. 3 Stan Wawrinka in the second round. Thiem was the youngest player to beat a top-three player since Juan Martin del Potro stunned Federer at the 2009 US Open.

His rankings trajectory is a screaming 45-degree vector on a chart, but the bare numbers are even more impressive. Entering the 2012 season, he was ranked No. 638 among ATP players, then more than halved it, to No. 309, a year later. Thiem began the 2014 season at No. 137 and now, after he has worked his way into so many main draws, he finds himself at No. 57 -- and an automatic qualifier for most big events.

The very first game offered a few glimmers of the future, when Thiem pushed Nadal to three deuces and took eight minutes off the clock. There were also killer forehand and backhand cross-court winners and a sublime half-volley drop shot for another winner.

Heading into the match, there was a sentiment among the tennis intelligentsia that Thiem might be able to sneak off with a set. In fact, he found himself up 3-1 in the third but could not consolidate the early break. No matter. He seems headed, at the very least, for the top 10.

Two months ago, before the tournament in Miami -- where, of course, he qualified and reached the second round -- Thiem chatted with ESPN.com. He was asked if the transition from juniors to professional tennis was harder than he thought it would be.

"Honestly, yes," he replied. "In the juniors you are kind of a star, but just because you are a good junior doesn't mean you will be a good pro. I did not play so well in the Futures a few years ago. Everybody wants to beat you out there. It took some time to learn how to play at that level."

He's already figured out how to beat some of the better guys who make a living in this game. After his training session with Professor Rafa, he's another step closer to understanding how to play with the very best.

"If he's a stock," Gilbert said, "put a buy on him."