MELBOURNE, Australia — There are two Rafael Nadal story lines swirling about during this first week of the Australian Open.

One involves the 20-time Grand Slam winner’s lower back, which, in his words, is not great, though it did not get in the way of his efficient, straight-sets win over Laslo Djere of Serbia in the first round Tuesday.

The second story line involves a 17-year-old Spaniard named Carlos Alcaraz who has suddenly become known as “the next Rafa.” Nadal’s decision to practice with Alcaraz last week, in the final days leading up to the year’s first Grand Slam, raised the volume of the hype surrounding the teenage prodigy.

And as Nadal was preparing for his first-round match, Alcaraz was pumping his fist to celebrate his first win in a Grand Slam tournament, over Botic Van de Zandschulp of the Netherlands, a solid 6-1, 6-4, 6-4 beating.

“He has intensity, he has the passion, he has the shots,” Nadal said of Alcaraz. “Then it’s all about how much you are able to improve during the next couple of years. It depends on how much you will be able to improve that will make the difference of whether he’s going to be very good, or if you’re going to be an amazing champion.”

Prematurely declaring a teenager a future legend is as much a part of tennis as fuzzy yellow balls. For several years Grigor Dimitrov of Bulgaria was called “Baby Fed” because his precocious creativity and all-around game resembled that of the Swiss great Roger Federer. That was nearly a decade ago. Dimitrov is now 29, ranked 21st and still looking for his first Grand Slam title.

There is always a yearning for the next big thing, and so the buzz around Alcaraz persists.

“It’s been a while since we had a young Spaniard came along like this with the promise he is showing at his age,” said Jim Courier, the former world No. 1 and a two-time champion in Australia, referring to when Nadal announced himself with a win over Federer at 17. The expectations are indeed a lot for Alcaraz to shoulder, Courier said, but Nadal once felt that pressure, and so have others. “I suspect Carlos will keep the blinders on pretty tight,” Courier said.

Alcaraz is hardly a Nadal clone. He does not hit with Nadal’s next-level topspin, and his coach, Juan Carlos Ferrero, said hardcourts would probably be his best surface rather than clay. Alcaraz shares none of Nadal’s on-court compulsions, such as making sure the labels of his water bottles face a certain way during matches or following a specific pattern as he walks to his chair on a changeover. But a Spanish player breaking out at 17 has implications.

Alcaraz beat David Goffin of Belgium, ranked No. 13, last week during a warm-up event in Australia, which kick-started the “next Rafa” buzz at Melbourne Park. Then he drew the ideal first-round opponent — Van de Zandschulp, a 25-year-old who has never sniffed the top 100 and looked the part as Alcaraz ran him around the court and pressured him into 73 errors.

Ferrero, the former world No. 1 who has been working with Alcaraz the past three years, said Alcaraz’s time practicing last week with Nadal and Andrey Rublev of Russia, the No. 7 seed, was a key to his success in the first round.

“He got to see what great players do,” Ferrero said.

That did not start out so well. Late last week, Alcaraz walked onto the court at John Cain Arena for a hitting session with Nadal, who immediately began pelting him with forehands and backhands, because Nadal practices as if he is playing a Grand Slam final, even when he has a sore back.

“He hits the ball very hard,” Alcaraz said of Nadal. “He tries to hit harder on every ball.”

Alcaraz struggled at first to keep the rallies going more than a few shots. Nadal did not relent. Alcaraz took a while to adapt to the pace.

There is no shame in that, since 17-year-olds are not supposed to be able to compete at this level of men’s tennis in 2021. The game is supposed to be too physically demanding for a teenager who is balancing professional tennis with his final year of online high school. But Alcaraz is already 6-foot-1 (the same height as Nadal), with broad shoulders and thick quadriceps muscles.

But Tuesday’s win was his first best-three-of-five-sets match. He still has the complexion of a high school senior, and he prefers Instagram to TikTok. He worships the soccer team Real Madrid (Nadal does, too), though he gave up organized soccer when he was 10 to focus exclusively on tennis. He lives mostly at Ferrero’s tennis academy in Villena, near Spain’s southeastern coast, roughly an hour by car from Alcaraz’s home in El Palmar, where he returns every other weekend.

Spain’s top men’s players, who dominated the top 50 not long ago and are still a force, have for years been a very close-knit group. They show up at one another’s matches and gather on the road to share meals and watch soccer.

As Alcaraz battled Van de Zandschulp on Tuesday, he kept looking over and pumping his fist in the direction of Ferrero and Pablo Carreño Busta, the No. 15 seed at the Australian Open. Carreño Busta is 12 years older than Alcaraz and has become something of a big brother to him at Ferrero’s academy.

Alcaraz played on Court 17, which is tucked in near a construction site, a busy railroad junction and the backsides of John Cain Arena and the Melbourne Cricket Ground. There are just a few hundred seats. It is Melbourne Park’s version of the boonies.

Alcaraz does not figure to have many more matches there, but just before he headed onto the court, Carreño Busta reminded him to take a minute to savor the start of his Grand Slam career.

“I was a little nervous,” Alcaraz said. “He told me to enjoy the moment.”

He did. He won the first set in 25 minutes, tormenting Van de Zandschulp with nasty overheads, endless hustle and timely breaks of serve, often when Van de Zandschulp seemed to have the game in hand.

“He’s very good, he’s very young,” Nadal said. “I really believe that he will have a great future because he’s a good guy, humble, a hard worker.”

Nadal, with his questionable lower back, will face Michael Mmoh of the United States in the second round Thursday. Alcaraz will play Mikael Ymer of Sweden. Both Mmoh and Ymer, neither of whom has made the third round of a Grand Slam, needed five sets to survive their first-round matches, not exactly ideal preparation for facing off against the real Rafael Nadal and the player considered his heir.

“It’s been a very fast progression for him, not that we are in a rush,” Ferrero said of Alcaraz. “This year I think he is going to make a really big step.”