South Korean sensation Hyeon Chung is through to his maiden grand slam semi-final after scoring a straight-sets victory over American surprise packet Tennys Sandgren 6-4, 7-6 (7-5), 6-3 in their unexpected Australian Open quarter-final at Rod Laver Arena on Wednesday.
Chung, the first Korean tennis player to make it to the final four of a major, will now face either Roger Federer or Tomas Berdych for a spot in Sunday night's final.
"Whoever win, I'm playing. I don't care," a jubilant Chung said.
Backing up from his stylish straight-sets victory over six-time winner Novak Djokovic, Chung showed no signs of a psychological letdown as he broke Sandgren four times on Rod Laver Arena to storm into the last four in two hours and 28 minutes.
Triumphant at the 2017 Next-Gen Finals in Milan, Chung has carried his blazing form to Melbourne, adding Sandgren to his growing list of scalps this fortnight that also include world No.4 Alexander Zverev, the German's brother Mischa who ousted Andy Murray last year and Sydney International champion Daniil Medvedev.
At 21 and 254 days, Chung is also the youngest men's grand slam semi-finalist since Marin Cilic at the 2010 Australian Open. The South Korean could meet the Croat who in this year's final.
The result brought to an end one of the most unlikely runs seen at Melbourne Park, with world No.97 Sandgren, who had previously never won a grand slam match, ousting fifth seed Dominic Thiem and ninth seed Stan Wawrinka on his way to becoming the first American to the Australian Open quarters since Andy Roddick in 2010.
Sandgren, 26, boasted total career winnings of $US488,735 prior to this event, having only previously won two Tour matches, but will now collect $A440,000 for making the final eight.
The Tennessee native gave one last gasp at the end as he saved five match points and brought up two break points while trailing 5-3, but Chung finally overcame his nerves to win the third set in 47 minutes.
"I don't know in last game 40-love up, I start thinking what I had to do in ceremony, something like that," Chung said.
"After the deuce point, no ceremony. I'm just trying to stay focused because I'm first time in these (big) matches."
While Sandgren displayed exquisite net play at times, 21-year-old Chung's superiority from the baseline was a decisive factor in the result.
Sandgren's inability to open up the court because of Chung's speed was also key and the American's poor service also made things easier for the Korean.
Heading into this match, Sandgren was 75 per cent for the tournament for first serves in, yet could only manage 55 per cent on Wednesday compared to Chung's 76.
Chung also had the ascendancy in percentage of second-serve points won (62-45).