Roger Federer made it through to a record seventh Australian Open final when South Korean Chung Hyeon retired in the second set of their semi-final.

The Swiss led 6-1 5-2 when 21-year-old Chung was forced to call it quits, three games after being treated for a blister on his left foot.

Defending champion Federer, 36, goes on to face Croatian sixth seed Marin Cilic in Sunday’s final.

The world number two is seeking a sixth Australian and 20th Grand Slam title.

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Federer was on course to take a two-set lead after just 62 minutes when the second semi-final came to an abrupt halt.

Chung’s management later said the problem had developed during the tournament, and they had tried to ease the pain with injections as it was “much worse than a regular blister”.

“I thought the first set was normal,” said Federer. “I couldn’t tell what was going on with my opponent.

“In the second set I felt he was getting slower. He’s had a problem with the blister. It hurts – a lot. At some point it’s too much and you make things worse.

“Clearly I’m happy to be in the final – but not like this. He’s had such a wonderful tournament.”

Chung had spent around 12 hours on court heading into the semi-final, including a gruelling win over Novak Djokovic in round four, and the physical effort finally took its toll.

Federer had established a commanding lead, winning the first set for the loss of one game despite only getting 32% of his first serves in.

The Swiss kept his cool after a brief disagreement with the umpire to swat away a backhand winner for a 3-1 lead in the second set, and Chung called for the trainer at the next changeover.

Heavy strapping was applied to the world number 58’s foot and he managed to hold serve on the resumption, but after Federer raced through his next service game, Chung approached the umpire and retired.

Federer extends his Open-era record to 30 Grand Slam final appearances and is one win from joining Djokovic and Roy Emerson on a record six Australian Open titles.

“I must admit, you do take the faster matches whenever you can because there’s enough wear and tear on the body,” said Federer.

“There’s enough tough matches throughout the season that when they happen, you take them.

“I’m just happy I’m in the finals, to be honest. That was the goal before the match today.”

Analysis – What chance Cilic?

BBC tennis correspondent Russell Fuller

The end came even more quickly than anticipated. Federer had been in total control, varying his length and spin, and denying a tense 21-year-old any rhythm in his first Grand Slam semi-final.

Both Chung, and Kyle Edmund on Thursday, would have had to play brilliantly even if fully fit to threaten a repeat of the Wimbledon final here in Melbourne. But their injury issues are another reminder of how difficult it is for younger bodies to withstand a full fortnight’s tennis at Grand Slam level.

Blisters undermined Cilic in July’s Wimbledon final, but the Croat could pose a significant danger to Federer’s hopes of a 20th Grand Slam title if fully fit.

Their head-to-head record doesn’t suggest much of a contest, but Cilic can draw inspiration from his one victory. He returned superbly in the US Open semi-final of 2014, won in straight sets, and went on to win the title.

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