Chung Hyeon became South Korea’s first Grand Slam semi-finalist with a straight-set win over American Tennys Sandgren at the Australian Open.

Chung, 21, won the surprise quarter-final between two unseeded players 6-4 7-6 (7-5) 6-3 on Rod Laver Arena.

The world number 58 is the youngest Grand Slam semi-finalist for eight years, and the lowest-ranked Australian Open semi-finalist for 14 years.

He will face Roger Federer or Tomas Berdych in the last four on Friday.

• Edmund’s rise towards the top – via South Africa, Yorkshire and the Bahamas
• Kerber thrashes Keys to reach semi-final
• Live scores, schedule and results
• BBC coverage times

Asked who he would prefer to play, a smiling Chung said: “I don’t know. 50-50, whoever wins, I’m playing, I don’t care.”

Britain’s Kyle Edmund and Croatian sixth seed Marin Cilic meet in the first men’s semi-final at 08:30 GMT on Thursday.

Chung had beaten fourth seed Alexander Zverev and six-time champion Novak Djokovic en route to the last eight, and found himself the favourite in his first Grand Slam quarter-final.

Across the net he faced an even more unlikely quarter-finalist in Sandgren, the 26-year-old world number 97 who had never won a Grand Slam match before Melbourne.

The pair had played in Auckland earlier this month, with Chung coming through in three sets, and he took charge once again.

After breaking serve immediately he served his way through the first set and into a 2-0 lead early in the second.

Sandgren, who has attracted as much attention for his social media presence as his tennis in recent days, appeared to be struggling but he staged an impressive comeback to lead 5-3 and serve for the set.

He could not close it out, however, a forehand into the net drawing Chung back to 5-5 and the Korean went on to edge the tie-break as he dictated with his forehand.

Chung won a lengthy game to break for 3-1 in the third set and secured the win after an entertaining final game in which he let a 40-0 lead slip, as Sandgren came up with some astounding reflex volleys.

Asked about that final game, Chung joked: “In 40-0 I was starting to think of what to do at the ceremony.”

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Two-time Grand Slam champion Angelique Kerber thrashed Madison Keys in just 51 minutes to reach the Australian Open semi-finals.

The 30-year-old German was in brilliant form as she beat American Keys 6-1 6-2 on Rod Laver Arena.

Keys, a 2017 US Open finalist, struggled badly throughout, winning only 18 of 46 points on her own serve.

Kerber, the 2016 champion in Melbourne, will play world number one Simona Halep or Karolina Pliskova in the last four.

• Edmund’s rise towards the top – via South Africa, Yorkshire and the Bahamas
• Live scores, schedule and results
• BBC coverage times

“Every game was close in the second set, I am just pleased to get through and be again in the semi-finals here,” said Kerber, who, including the Hopman Cup team competition, has won all 14 of her singles matches in 2018.

“I really enjoy my tennis right now.”

Keys, seeded 17th, had served 26 aces in her first four matches in Melbourne but did not manage a single one against the 21st seed.

Eight unforced errors in the first three games set the tone as Kerber raced through the first set and established a 3-0 lead in the second.

Keys broke to love to get back on serve at 3-2 but an errant forehand caused to fall behind again and Kerber closed out the victory by breaking the American for the sixth time.

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