Dubbed the 'Professor,' history maker Hyeon Chung walked away from Rod Laver Arena at the Australian Open with straight As.
Chung upset one of the Australian Open's most successful players, Novak Djokovic, in a fierce 7-6 (7-4) 7-5 7-6 (7-3) battle that repeatedly had the crowd on its feet Monday thanks to an abundance of breathtaking, extensive rallies.
Novak Djokovic loses to Hyeon Chung in straight sets
Chung wins 7-6 7-5 7-6
Tennys Sandgren upsets fifth-seed Dominic Thiem
Roger Federer, Simona Halep, Angelique Kerber advance
Indeed with Chung's athleticism and ability to produce big shots on defense, Djokovic could have been forgiven for thinking he was playing a younger version of himself.
The 21-year-old Chung became the first South Korean to ever make a grand slam quarterfinal, quite the memorable sporting achievement weeks before the nation will be in the spotlight hosting the Winter Olympics.
"I'm just trying to copy Novak because he is my idol," Chung, who earned the nickname because he is one of tennis' few players to wear glasses, told the crowd afterward. "Dreams (came) true tonight.
"Yeah today victory for my country, I think tennis coming up after this tonight," he later told reporters.
The world No. 58 thus proved his win over fourth-seed Alexander Zverev was no fluke and he'll be favored to next beat another surprise quarterfinalist, Tennys Sandgren.
The 97th-ranked American stunned fifth-seed Dominic Thiem 6-2 4-6 7-6 (7-4) 6-7 (7-9) 6-3 after the Austrian saved a match point in the fourth set tiebreak with a courageous backhand down the line.
Trailed in each set
Early deficits proved too much for Djokovic to overcome against the tenacious Chung.
The six-time champion in Melbourne fell behind 4-0 in the first, 4-1 in the second and 3-1 in the third.
Seeking the respite of another tiebreak in the second at 5-6, the tennis gods certainly assisted Chung with a net-cord winner on the opening point. Djokovic rallied in the game but became unhinged when contributing a double fault on game point.
In the third-set tiebreak Djokovic trailed again, 3-0, got back to 3-3, only to witness Chung engineer yet more magic by delivering a curled forehand passing shot winner that lit up the stadium.
Overall Chung was the more efficient on break points, going 6-for-10 to Djokovic's 5-for-19.
"We do play very similar," said Djokovic. "He definitely has the game to be a top-10 player, without a doubt. How far he can go, that depends on him.
"Obviously I respect him a lot because he's a hard worker, he's disciplined, he's a nice guy, he's quiet. You can see that he cares about his career and his performances. So I'm sure that he's going to get some really good results in the future."
Despite his pedigree even Djokovic probably wouldn't have expected to leave Melbourne with the title given this was his first tournament since being sidelined by a right elbow injury at Wimbledon in July. Instead his first priority simply would have been to depart Australia healthy.
But that won't be the case. Djokovic took a medical timeout due to the elbow and said it affected his serve, which he's tweaked following the elbow issue. He'll assess what to do next with his entourage that includes coaches Andre Agassi and Radek Stepanek.
"Kind of end of the first set it started hurting more," Djokovic told reporters. "So, yeah, I had to deal with it till the end of the match.
"I was hoping I can go through it. As I was mentioning before, as a professional athlete, you have to deal with pain at a certain level, a certain degree. You kind of get used that.
"But, yeah, I don't want to talk about my injury tonight because then I'm taking away Chung's victory, the credit that he deserves.
"He just played, in the clutch moments, some really high-quality tennis."
Another top-10 win for Sandgren
So did Sandgren, who had never even won a grand slam match prior to this fortnight.
If his victory over three-time grand slam winner Stan Wawrinka in the second round didn't raise eyebrows -- the Swiss himself hadn't competed since Wimbledon because of a knee injury -- there was no asterisk needed Monday.
In another milestone for the 26-year-old, Sandgren played -- and won -- his first ever fifth set.
"Obviously the first three matches were more than I expected," said Sandgren. "This one was about as hard-fought as I've ever had a match before. My biggest match, as well, pretty neat.
"I definitely had a real pinch-me moment. Wow, this is hopefully real, you know. If I wake up now, I'm going to be real upset."
The only negative for Sandgren? His mom Lia suffered a cracked rib back home over-celebrating one of her son's wins in Melbourne.
"I've got like a neighborhood, core neighborhood group, with my mom," said the Tennessee native. "They watch a lot of my bigger matches.
"They'll go in the basement, put the match on the projector screen on the bottom. (There is) a pool table down there, as well. They were jumping up and down, celebrating. She fell onto the pool table, cracked a rib."
Nothing that dramatic happened to men's defending champion Roger Federer -- who could have faced Djokovic in the semis -- and women's No. 1 Simona Halep.
Federer and Halep cruised in straight sets over Marton Fucsovics 6-4 7-6 (7-3) 6-2 and Naomi Osaka 6-3 6-2 respectively. To reach the semifinals, Federer must beat perennial Australian Open quarterfinalist Tomas Berdych. His chances are good, since he owns a 19-6 record against the Czech and is 4-0 at Melbourne Park.
The Romanian -- who challenges former No.1 Karolina Pliskova in the last eight -- must have been especially pleased to breeze through because she spent nearly four hours on court Saturday in a record win over Lauren Davis.
Angelique Kerber meanwhile needed three sets to overcome the unorthodox game of Hsieh Su-wei 4-6 7-5 6-2. Kerber, the former No. 1 and 2016 Australian Open winner, won her 13th straight match to begin 2018 after a dismal 2017.
Kerber next meets US Open finalist Madison Keys, who has quietly progressed to the last eight without dropping a set. Keys thumped eighth-seed Caroline Garcia of France 6-3 6-2.
But in truly announcing himself to the tennis world, Monday belonged to Chung.