Melbourne - Roger Federer is figuring out how he will play South Korean unknown quantity Chung Hyeon ahead of Friday's semi-final in one of the Australian Open's most intriguing match-ups in years.
On paper it looks hugely one-sided. Federer, a 19-time Grand Slam champion and veteran of 382 Slam showdowns over 20 years, up against an unseeded 21-year-old lining up for just his 17th match at a major.
It's been a breakthrough tournament for Chung, whose 58th ranking is expected to tumble after toppling six-time champion Novak Djokovic and world No 4 Alexander Zverev on the way to becoming the first South Korean to reach the last four at a Grand Slam.
The Swiss defending champion is a master at working out his opponents and coming up with solutions. Chung will be no different.
"I hardly know Chung. I've hardly spoken to him," Federer said after Czech-mating Tomas Berdych in the quarter-finals.
"Right now I couldn't tell you how I need to play him. One thing I know is I'm going to be playing aggressive.
"I don't know exactly how he returns and how he serves exactly. Those are two major aspects to the game. I have to figure that part out a little bit."
Federer and his brains trust will comb through Chung's matches in Melbourne, but the five-time Australian Open champion has been impressed with the bespectacled Korean's tournament.
"I'm very excited to play Chung. I thought he played an incredible match against Novak Djokovic," he said.
"I mean, to beat him here is one of the tough things to do in our sport. To close it out, that was mighty impressive.
"To bounce back from a Novak match and just somehow get it done in the quarters, that's tough. That shows that he's had good composure, a great mindset.
"I think it's an interesting match for me," added Federer, lining up for a record 14th Australian Open semi-final.
Chung has made history by becoming the first South Korean to reach a Grand Slam semi-final and is also the lowest-ranked player in 14 years to get to the last four in Melbourne.
He has limited English but the Australian crowds have taken to him during his candid on-court interviews.
"I'm really surprised because I really don't know. I make semis, I beat like Sascha (Zverev), Novak, the other good players. I never playing in second week in Grand Slam, so I'm really surprised," Chung said.
He won the 2015 ATP Most Improved Player award and signalled his coming of age with his big breakthrough at the 'NextGen' ATP finals in Milan where he beat Russia's Andrey Rublev in November.
Chung will become the highest-ranked South Korean player in history after the Australian Open when he will break into the top 30 and could zoom as high as No 10, if he wins the tournament.
The Korean, who has modelled his game on childhood idol Djokovic with his elastic sliding ability of using the hard court as a clay court, has been dubbed "The Professor" due to his trademark thick white-rimmed glasses after being diagnosed with weak eyesight.
"He just loves the environment," Chung's South African coach Neville Godwin said.
"It's pretty exciting for him and he's a youngster. It's really great how he's allowing his character and his personality to come out.
"He's got so much skill, so much talent and he's been in this situation so many times that it's really about keeping things very simple and control what you can do."