MELBOURNE - He's modest, quiet, unflashy, with a cool, gentle swagger, so let's find a simple, uncomplicated word for him. A word that fits. A word that says enough. A word like tough.

Behind those plastic spectacles, a man of mettle, only 21, born in Suwon and unveiled officially to the world on a Melbourne night. Clap. Whistle. Say "dae dan ha se yo". In Korean, a writer tells me, it roughly means great.

Let's first thank Chung Hyeon for mocking Asian stereotypes. Yeah, yeah, he looks like a geek but plays like a giant. He even likes his nickname, The Professor, and that's because it kind of suits him. The athletic academic. Whose shoes should be investigated for wings and wheels.

He's steady and sturdy but let's also give him points for style, especially that outrageous cross-court forehand pass from the corner with Novak Djokovic sitting on the net in the third-set tie-breaker and then gesturing coolly to the crowd as if to say, 'let's hear you'. He heard them.

Later, it was sweet of Jim Courier to hand him the microphone to speak to his fans and his nation in Korean, but it's the unyielding language his racket speaks which has everyone in a tizzy.

His ranking is No. 58, which is clearly fake news, but he was - says Baek Seungwon of Tennis Korea - the No.1 searched item on Monday evening on Naver which is the South Korean search engine. He's also clearly smart, for the second question after his Djokovic match was about South Korea, North Korea and the Winter Olympics which he sensibly sidestepped. Dude is here for forehands not foreign policy.

He's so tall that already today three people have asked me, "really, he's 1.88m?", and he comes from a tennis family, all of whom are here, and he doesn't have a girlfriend - someone asked, as if that is relevant - but what matters most is not his Park Ji Sung-lungs or his accuracy which is almost as fine as another Korean's, the Olympic champion archer, Im Dong Hyun, who just by the way also has imperfect vision.

No, what matters is that word. He's tough.

All Monday night, Djokovic reeks of the beautiful desperation of champions. He's powered by pride, past pain, trying to remember who he used to be, not yet ready to go home, not caring if he makes the injury worse because wanting to win is like an ache. He must believe in a crevice of his brain that if he pushes the Korean, then, as has happened so often before with so many surging players, eventually they fade, they don't have anything left, they can't sustain their standard or stretch their nerve any more.

But Chung won't wilt, fold, droop, shrivel, collapse. Maybe there's no word for it in Korean. He has a friend who travels with him occasionally to teach him English, but this he's learnt himself.

In the first set he leads 4-0 and Djokovic makes it 5-5; in the second set he's 3-0 and the Serb makes it 4-4; in the third he's 3-1 and his rival evens the score. Every time Chung is pushed he doesn't panic, he finds a shot and a solution, not intimidated by court, afraid of occasion or daunted by idol. It's majestic and magnetic all at once.

Tough is what Alexander Zverev said a few rounds earlier but we weren't completely listening then. "(Chung is) one of the toughest guys, full stop ... When he plays like that, there are very, very few people who will beat him."

Tough is what Djokovic, who found grace amidst pain, called Chung, repeatedly, after Monday night. First he says: "Whenever he was in trouble, he came up with some unbelievable shots, passing shots. Just from the back of the court, you know, he was like a wall." Then he says: "He just played, in the clutch moments, some really high-quality tennis." After that he adds: "He just was mentally tough and patient."

Of course, it's early days yet and tough has to be more than a single match. It has to become a signature. But he has people's attention for this wasn't a flashy feat or a big-serving show (his fastest was a modest 193kmh), but a resilient, self-possessed introduction to who he might be. It wasn't kid stuff, but a 21-year-old in a planet of 30-plus champions producing an assuredly adult performance.