'Unbelievable': Tennis world stunned by qualifier's 53-year first

Australian Open qualifier Aslan Karatsev has continued his stunning run through the tournament, advancing to the semi-finals after defeating Grigor Dimitrov in four sets.

The Russian world No.114 pulled off his latest upset after Dimitrov, who was the 18th seed, was hampered by a back problem after winning the first set 6-2.

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Dimitrov was on top early in the second frame before Karatsev stormed back into contention, winning the next three sets in convincing fashion.

Karatsev's victory made him the first player to make it to the final four on their grand slam debut in 53 years.

The 27-year-old Russian will face one of countrymen Andrey Rublev or Alexander Zverev in the semi-finals, saying it was an 'incredible' feeling.

"It's an unbelievable feeling, of course. The first time playing a main draw, first time playing the semis. It's incredible," Karatsev said.

"It was a really tough one at the beginning for me, to hold the nerves, and it was really tricky. The heat was too much.

"I tried to play in the second set. I tried to find a way how to play, and then in the third set it felt better."

Karatsev he didn't notice Dimitrov was hampered by his back problem until the Bulgarian star's serve slowed to just half its normal pace.

The rising star's performance earned him plenty of plaudits on social media.

Tsitsipas' armchair Open ride may be over

If not for Thanasi Kokkinakis, Greek showman Stefanos Tsitsipas would barely have raised a sweat on the way to his Australian Open quarter-final showdown with history-chasing Rafael Nadal.

The No.5 seed dropped a total of just 10 games in his first and third-round wins over Gilles Simon and Mikael Ymer.

And he didn't even get to set foot on Rod Laver Arena on Monday night after his fourth-round opponent and No.9 seed Matteo Berrettini withdrew with an abdominal strain.

So if Nadal is looking for any recent pointers on how best to stretch Tsitsipas he would be well advised to study the second-round clash at Melbourne Park where Kokkinakis was just shaded in a five-set thriller stretching over four and a half hours.

The Spanish world No.2 pulled out of the ATP Cup earlier this month with a back injury.

Nadal's form and fitness have both improved as the Open has progressed, and he rated the opening set of his fourth-round win over Italian Fabio Fognini as the best tennis he has played this year.

"That's normal because I was able to practise for two days in a row," said Nadal.

"That makes an important difference.

"But at the same time it's important to find positive feelings now.

"My physical condition needs to keep improving but I think this match (against Fognini) helps, too.

"I was not able to practise the proper way for the last 19 days, but yesterday I started again to increase the amount of work on the practice court and today has been a positive victory with some long points."

With AAP

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