Melbourne - History-making Chung Hyeon became the first South Korean to reach a Grand Slam semi-final and the lowest-ranked player in 14 years to get to the last four at the Australian Open on Wednesday.
Ranked 58, he needed six match points before completing a clear-cut 6-4, 7-6 (7/5), 6-3 win over unseeded American Tennys Sandgren on Rod Laver Arena in 2hr 28min.
He will face either defending champion Roger Federer or Tomas Berdych in Friday's semi-final.
In beating Sandgren, Chung, 21, became the first man or woman from his country to make the last four of a Grand Slam and the lowest-ranked men's semi-finalist in Melbourne since Russia's Marat Safin (No 86) in 2004.
The rising star joins Briton Kyle Edmund as the first unseeded men's semi-finalists in Melbourne since Frenchman Jo-Wilfried Tsonga in 2008.
His achievement comes after his monumental wins over six-time champion Novak Djokovic and world No.4 Alexander Zverev to herald his arrival to big-time tennis.
"I'm really surprised to make the semis, I beat Sascha (Zverev), Novak and other good players. I have never played in the second week at a Grand Slam," he said.
Chung said he was inspired by Japan's Kei Nishikori, the 2014 US Open finalist, who blazed the trail for Asian tennis.
"All Asian players look to Kei and we are trying to follow him. He's the pride of Asian players," he said.
Asked who he wanted to face in the semi-final, Federer or Berdych, Chung replied diplomatically with a smile: "It's 50-50. They're two really good players, so I don't know who's going to win."
Chung had a few nervy minutes before he sealed the victory.
In a tense 11-minute final game he closed it out on his sixth match point after Sandgren threw everything at the South Korean to stay in the match.
"I think in the last game many things come together. If I win one more point, I make history in Korea. I was thinking like that," Chung said.
"I was thinking about the ceremony, something like that. Anyway, I tried to stay calm because the match was not finished."
Nicknamed "The Professor" due to his trademark thick white-rimmed glasses, he showed the benefit of his improved net play despite preferring to operate from the baseline.
"I'm just trying to work on playing on the net. In the pre-season and all the time when I practice, I'm just trying to play more at the net," said Chung, who won 21 points off 27 trips to the net against Sandgren.
"If I go to the net, I can save more energy."
Chung, who won the 2015 ATP Most Improved Player award, jumped out of the blocks with an early break before taking the opening set in 37 minutes, serving at a high 85 percent.
His play from the baseline took reaction time away from the American and helped him control the points.
Chung broke in the opening game of the second set with an exquisite backhand across the net clipping the line.
But Sandgren began to get more into the contest and broke back in the fourth when Chung's forehand was wide.
Sandgren broke again in the eighth and was serving for the second set before he was broken with a netted forehand.
Chung maintained his level in the tiebreaker getting to set point before he forced a Sandgren forehand long.
Chung broke in the fourth game of the final set and but temporarily his victory charged was held up before he got home on his sixth match point.