The defending champion was leading 6-1, 5-2 and in full control when Chung retired with foot blisters, bringing the curtain down on a breakout tournament in which he announced himself as a future star in the making. 

The 21-year-old sent 12-time Grand Slam winner Novak Djokovic packing in the quarter-finals, although the Serb was carrying an injury and not at his best.

But he also accounted for fourth seed Alexander Zverev in his best Grand Slam showing so far.

In 20 years at the top, Federer has seen plenty of players come and go and only had praise for the youngster.

“I think he is already a great player, but we are talking next level excellence and I think he will achieve that,” said Federer, who is into his 30th Grand Slam final as he chases a 20th major title.

“We will see much more of him. Top 10 for sure.”

He added that he did not want to put too much pressure and expectation on Chung as “I don’t think it’s fair”.

But he said: “I think he’s going to have a lot of success. At what stage, how much, we will see.”

Chung’s unexpected run to be the first South Korean in a Grand Slam semi-final has drawn new fans to the sport in his homeland where tennis lags far behind golf and baseball in the popularity stakes.

It also sparked top television ratings and a spike in sales of tennis gear, with Chung set to return home far more famous, and richer, than when he left.

– Red raw -Many Koreans were glued to their televisions watching him on Friday, with fan Park Meing-Cheon brought to tears in Seoul.

“Unfortunately, with the blister wounds on his toes, I couldn’t help crying earlier on,” she said.

Yoon Ji-Su, from Anyang City, forecast great things from him moving forward.

“Although the injury is a pity, I hope he recovers well, and I believe there will be great results in the next French Open, Wimbledon, and US Open,” he said.

Nicknamed “The Professor” due to his trademark thick white-rimmed glasses, Chung said he retired because his blisters were “red raw”.

Despite the anti-climax, he said it was great experience and he was “really honoured” to be on the same court as Federer.

“I enjoyed the two weeks, on court and off court. I’m just really happy,” he said.

“For sure, I played really good in the last two weeks. I made first round of 16, quarters and play Sascha (Zverev), Novak, Roger. I had a really good experience. 

“I think I can play better and better in the future.”

One of his key takeaways was the confidence it had given him.

“A lot of confidence. I played a lot of good players in the last two weeks. I can play, like, more comfortable on the court with the great players like Roger.” DM