Hyeon Chung's star continues to rise in Melbourne. Photo: Hyeon Chung on Twitter

MELBOURNE – Nightmares loom for players dreaming of Grand Slam success if they have the misfortune of running into bespectacled bogeyman Chung Hyeon in coming years, according to his coach Neville Godwin.

South Korea’s new sensation became his country’s first Slam semi-finalist yesterday with a 6-4, 7-6(5), 6-3 defeat of Tennys Sandgren, proving a waking bad dream for the 97th-ranked American.

Like victims Alexander Zverev and Novak Djokovic before him, Sandgren hammered away desperately at Chung, only for the unseeded Korean to keep returning with zombie-like resolve.

Unspoken of before the tournament among the lists of contenders, let alone the top young guns, Chung will battle defending champion and 19-time Grand Slam winner Roger Federer in one of the more unlikely semi-final match-ups.

“Obviously he moves around the court incredibly well and he’s incredibly flexible,” said South African Godwin, who began working with the 58th-ranked Chung last year. “Everyone has their strengths, but for Hyeon, I think it would be a nightmare to play against him because he basically 'out-Djokovic-ed' Djokovic (on Monday) which is something that not that many people have been able to do.”

Chung’s blazing run through the Melbourne Park draw has appeared like a bolt from the blue on the surface, but the 21-year-old has shown flickerings of promise for a number of years.

The parts have all clicked in a devastating way in Melbourne over the past fortnight, but the best is very much yet to come as he matures and enjoys more structure to his scheduling.

“We have changed some technical things on his serve, which he’s a lot more comfortable with now,” said Godwin, who ended his partnership with big-serving compatriot Kevin Anderson last year. “He has the option now of serving a high percentage or getting a free point or going for an ace... and he’s feeling a lot better about that.

“It’s not quite the finished product yet; it’s still quite a work in progress but that’s definitely an improved effort. I’d also like to see him use his phenomenal speed to get up the court a little bit more and use it more in offence rather than only on defence.”

Nicknamed “professor” for his scholarly look, Chung has shown humour on court, working the crowd with a hand-flapping celebration.