Defending champion Federer moved to within one win of a 20th Grand Slam singles title on Friday night when Hyeon Chung retired in the second set of their Australian Open semifinal.

He was leading 6-1, 5-2 when the 21-year-old Chung quit because of blisters on his left foot -- or "blisters under blisters under blisters," according to his agent.

Going into the match with Chung, Federer had won six of his 13 semifinals at Melbourne Park.

After 1 hour and 2 minutes with the roof closed on Rod Laver Arena, he's now 7-7. (He's well above the 50-50 mark at the other majors -- 11-1 at Wimbledon, 7-3 at the U.S. Open and 5-2 at Roland Garros.)

"I've played with blisters in the past a lot, and it hurts a lot. And at one point, it's just too much and you can't take it anymore -- you can't go on," Federer said. "That's why this one feels bittersweet. I'm incredibly happy to be in the finals, but not like this.

"He's played such a wonderful tournament, so credit to him for playing so hard again today."

Federer's conversation rate is better in finals in Australia -- the only time he lost a championship match was against Rafael Nadal in 2009.

He faces No. 6-seeded Marin Cilic on Sunday in what will be his record seventh Australian Open final and 30th at a Grand Slam.

Cilic was hampered by blisters when he lost to Federer in last year's Wimbledon final, but he has made a relatively pain-free run through the other half of the draw, including a quarterfinal win over an injured Nadal.

The 21-year-old Chung had an incredible run at Melbourne Park, becoming the first Korean to reach a semifinal at a tennis major and attracting plenty of attention for beating No. 4-seeded Alexander Zverev in the third round and upsetting six-time Australian Open champion Novak Djokovic in the fourth.

Roger Federer will face Marin Cilic in Sunday's Australian Open final for a chance at his 20th Grand Slam title. Mark Kolbe/Getty Images

But it took a toll. He needed a pain-killing injection before the match, and a medical timeout to re-tape his left foot after going down a break in the second set. He only played two more games before he quit.

"I think I did right thing. If I play bad on the court, it's not good for the fans and audience as well," he said. "I really hurt. I can't walk no more."

Federer predicted a bright future for Chung, who also will be more prepared next time for the rigors of the best-of-five set tennis at the Grand Slams.

"For sure. I play really good in last two weeks. I make first Round 16, quarters and semis -- I play (Zverev), Novak, Roger. I really good experience in last two weeks," he said. "I think I can play better and better in the future."

Federer started to sense something was wrong with Chung by the movement of his rival, and he was utterly dominant until that point.

After all, the 36-year-old Swiss star had the standing of the so-called Big Four to protect -- there hasn't been a final at Melbourne Park since 2005 that hasn't featured Federer, Nadal, Djokovic or Andy Murray.

Stan Wawrinka's win over Nadal in 2014 was the only final since 2008 that didn't feature two of the Big Four.

Cilic beat top-ranked Nadal in the quarterfinals and Chung stunned six-time champion Djokovic in the fourth round. And Murray, a five-time Australian Open runner-up, withdrew from the season-opening major to have surgery on his hip, leaving their collective reputation for dominance in Australia on Federer.

He didn't let anyone down in a clinical dismantling of the No. 58-ranked Chung, who won the Next Gen ATP Finals last November.

Earlier, Timea Babos of Hungary and Kristina Mladenovic of France became the first players from their respective countries to lift the Australian Open women's doubles crown.

Babos and Mladenovic combined to beat the Russian pair of Ekaterina Makarova and Elena Vesnina 6-4, 6-3.