MELBOURNE, Australia -- Naomi Osaka, who, as of Monday, will be the No. 1 tennis player in the world, has a habit of doing extremely grown-up things -- at least on the tennis court.

Saturday night at the Australian Open, she defeated Petra Kvitova in three tension-filled sets to capture her second straight Grand Slam title, just four months after winning the US Open.

After taking the opening set, Osaka had the title in her grasp. In the second set, she was up 5-3 and love-40 with triple-championship point on Kvitova's serve. But the Czech not only held, she won the next four straight games. In many cases, such a situation could have sent a player into a freefall, especially a player as young as Osaka. At 21, she is still young enough that if she tries to rent a car almost anywhere in America, she will have to pay a surcharge.

"We're used to seeing players go away after losing such a big lead," explained Courtney Nguyen, a senior writer for WTA Insider who has been covering tennis for more than a decade. "Especially against Petra. Petra has these comebacks in the second set and then the third set is like, 6-0 or 6-1. She just runs away with it because you're so demoralized."

Osaka, on the other hand, is unique in her ability to rally herself after disappointments. And disappointed she was -- she went into the locker room crying after losing the second set. Somehow, Osaka has the fortitude of a grown-up. An extremely zen grown-up.

Ultimately, she regrouped and pulled away, winning 7-6 (2), 5-7, 6-4.

But if you ask her about it, Osaka says she doesn't feel like a grown-up.

"I'm not sure if it's feeling grown up or being able to dissociate my feelings," she said afterward. "I don't know if that makes sense. Like, you know how some people get worked up about things? That's a very human thing to do. Sometimes, I don't know, like I feel like I don't want to waste my energy doing stuff like that. I think about this on the court, too. In the third set of my match today, I literally just tried to turn off all my feelings. So that's why I wasn't yelling as much in the third set. I'm not sure if that makes me grown up. I don't think so."

At just 21 years old, Naomi Osaka now has two Grand Slam titles. JEWEL SAMAD/AFP/Getty Images

The last person to win her first two Grand Slams back-to-back was Jennifer Capriati in 2001. She won the Australian Open and then the French. Capriati was 24. Osaka is 21. Last year, at the same tournament, Osaka was No. 72 in the world. Now she's leaving as No. 1.

Kvitova won her first Grand Slam title at Wimbledon in 2011 when she was 21 as well. It took her another three years to get the second, also at Wimbledon. She recalled what it was like to win the first one.

"For me was kind of big thing happened when I was young," Kvitova explained. "I didn't really know what everything is about. For me was a big surprise. I probably wasn't really ready to win it, to be honest. I wasn't really prepared. It took me a while to kind of get used to. Yeah, I think it's always a bit pressure from outside, as well, from yourself. You just want to play better. You're thinking like you have to win every single match because you just won a Grand Slam. That's how I was thinking actually. Yeah, I put a bit more pressure than I should.

"You just need to get used to the attention as well. Every time you are stepping on the court, you are kind of favorite of the match. The other players just want to beat you because you're playing well."

Osaka tried to describe what the tennis-watching audience sees as a unique poise and maturity that allows her to come back from game-point losses that would psychologically decimate other players, even veterans.

"I just felt kind of hollow, like I was a robot sort of," she said. "I was just executing my orders. I don't know. Like, I just did what I've been practicing my whole life in a way. I didn't waste any energy reacting too much."

Osaka sounded a lot like "Late Show" host Stephen Colbert in a 2011 interview with Terry Gross, describing what it was like to perform in "Company on Broadway," knowing that composer Stephen Sondheim is a stickler. In a way, it's almost like a sleeper cell: You just have to turn your brain off and rely on your training to kick in by instinct. Colbert had gone through hours of intense singing lessons, which he described as "yoga but for the inside of your body."

"You spend a lot of time thinking about your soft palate and opening up your sinuses, and it is almost impossible for someone to explain why that's important, how you can turn your head into a bell," he said at the time. "And then you have to forget all of it and sing, or as -- my voice coach is Liz Caplan, and Liz would say -- we would work and work and work. We worked for months. And then she said, 'Oh, just sing, stupid.'"

As Osaka talks about playing tennis, it seems she experiences something similar, except instead of "just sing, stupid," it's "just play, stupid."

Her ability to revert to her training is a remarkable and rare talent. It's what makes Naomi Osaka a two-time Grand Slam champion.