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. When you look at the two weeks that Cilic had at Wimbledon a year ago, where he made the final, he felt that that was the best tennis he was playing in his career.
The South Korean had taken a medical timeout earlier in the second set to receive treatment on his foot.
So now, with Federer marching through the Australian Open to reach this weekend's final against Cilic, we shouldn't really be surprised by what he is doing.
"The way he came out against me was very much a winner's attitude", Federer remembered. She saved match points against not one, but two opponents at Melbourne Park - Lauren Davis in the third round, and two-time major victor Angelique Kerber in the semifinal.
Making matters worse is the broadcaster robbed fans of roughly two-to-three games in a second set that only lasted a total of seven games before Chung was forced to retire.
While a defeat is naturally disappointing for Chung, he is set to get a huge boost in the ATP rankings thanks to his performances, moving up into the top 30 players in the world.
He had previously conquered Federer in three sets in the semi-finals on the way to his 2014 US Open triumph.
1 - First time in final for Simona Halep, for Caroline Wozniacki, and for Marin Cilic.
The 29-year-old Croat may stand between Federer and a 20th Major title as the underdog, but it is to be noted that Cilic overcame his opponent on the way to winning the 2014 US Open final.
Federer, naturally, expresses respect for Cilic, and even warmth, revealing they played together when they learned they were staying nearby on holidays in the Maldives in late November. One thing I know is I'm going to be playing aggressive.
"Clearly I'm happy to be in the final - but not like this". This time around, I'm a different player, different person, slightly different game, slightly different understanding of the game and different mental processes during the matches.
"I think overall consistently I'm playing better", he said.
"After two days, he wrote to me, "I'm here, too, in case you want to catch up and stuff, let me know".
Chung received a smattering of boos after retiring, though the crowd at Rod Laver Arena applauded as he walked off court.
So what would grand slam title number 20 mean? "I've hardly spoken to him", the five-time Australian Open champion said.
"I'll definitely have to look into how I need to play against him because he has some great qualities, especially defensively, like Novak has", Federer said. Later in the year, Federer would capture his seventh Wimbledon title for Grand Slam title No. 19. The Dane had to dig deeper than she ever has in Australia to come back from losing eight straight points near the end of the second set to fight her way to a 7-2 tiebreak win that clinched the match.