Defending champion Roger Federer strolled into the Australian Open final in a bitter-sweet win after Chung Hyeon's retired injured in their semi-final on Friday.
The Swiss star was leading 6-1, 5-2 when the South Korean called it quits with foot blisters and will now face Marin Cilic in Sunday's final.
Chung, the first South Korean man or woman to play in a Grand Slam semi-final, was treated in a medical timeout for the left foot problem two games earlier.
But it came as a big surprise when the 21-year-old walked to the net at 30-30 and trailing 2-5 after 1hr 02mins in the second set to concede defeat.
It put Federer into his seventh Australian final as he chases his sixth Melbourne title and 20th Grand Slam victory.
Federer leads 2014 US Open champion Cilic 8-1 in their meetings.
The Swiss maestro now has a 30-13 win-loss record in Grand Slam semi-finals and has yet to drop a set in this year's Australian Open.
"You couldn't tell until the end," he said of Chung's injury problems. "That's probably why a lot of people are stunned (he retired).
"I could tell something was wrong before he took the injury timeout, but he has a great composure.
"I think he is already a great player, but we are talking next level excellence and I think he will achieve that.
"We will see much more of him. Top 10 for sure. The rest we will see."
It was a muted semi-final with the Rod Laver Arena retractable roof closed for rain further improving Federer's chances given his indoor record.
He broke Chung's opening service and twice more to romp away with the first set in just 33 minutes as the Korean made a flurry of errors.
It got no better in the second set with Federer again breaking in the fourth game before the trainer was called on to the court to treat Chung for his foot blisters.
Chung only lasted a bit more than two games before pulling out to a stunned silence.
"In the second set I felt he was starting to get a bit slower, fighting with a blister," Federer said.
"I've played with blisters in the past a lot, and it hurts a lot, and at one point it is just too much and you can't take it anymore.
"That's when you realise there is no way you can come back and you make things really worse, it is better to stop. That's why this feels bitter-sweet.
"Obviously I'm incredibly happy to be in the finals, but not like this."
Federer broke Chung's serve four times off 11 break points and only had one break point on his own service.
The Swiss second seed hit 24 winners while Chung made 17 unforced errors in 14 games, eight of them off his normally potent forehand.
Federer faces Chung hurdle to 30th Slam final
Roger Federer steps on court against new South Korean star Chung Hyeon Friday with the prospect of an Australian Open final against Marin Cilic at stake.
The hugely experienced Swiss ace is an overwhelming favourite as he targets a 20th Grand Slam title, but the unseeded 21-year-old has already sent Novak Djokovic packing, proving anything can happen.
Cilic is already through to his first ever decider at Melbourne Park after sweeping past Britain's Kyle Edmund in three comfortable sets in his semi-final on Thursday.
Simona Halep and Caroline Wozniacki will face off for the women's crown on Saturday in a clash that will also determine the world number one ranking.
Defending champion Federer is playing a record 14th semi in Australia and aged 36 shows no sign of surrendering his long invincibility, with a record 30th Grand Slam final beckoning.
He is the oldest man to reach the last four here since Ken Rosewall (42 years) in 1977.
Federer admitted he knew little about Chung and needed to do some homework, but was wary after he upset Djokovic.
"I'm very excited to play Chung. I thought he played an incredible match against Novak," he said ahead of their evening showdown on Rod Laver Arena.
"I mean, to beat him here is one of the tough things to do in our sport, I believe."
It has been a breakthrough tournament for Chung, whose 58th ranking is expected to tumble after toppling not just six-time champion Djokovic but world No.4 Alexander Zverev.
He is the first South Korean to reach the last four at a Grand Slam and excited at the prospect of playing Federer, who is yet to drop a set.
"I'm just trying to play the same all the time. I'm just trying to fight 100 percent," he said.
If Federer, who is chasing a sixth Australian title, gets through, he will fancy his chances against Cilic. He holds an 8-1 record against the Croat, including victory in the 2017 Wimbledon final.
Cilic has beaten Chung on all three occasions they have played, most recently in Brisbane in 2016.
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