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Marin Cilic is through to the semifinals after a dramatic five-setter.
World number one and 2017 runner-up Rafael Nadal was struggling with an injury in his right thigh and after a medical time-out in the fourth he had to retire in set five.
„Tough moments“, the Spaniard said. „But it´s not the first time an opportunity is gone for me.“
But it was only the second time Nadal had retired in more than 250 Grand Slam matches.
„In the end very fortunate, because Rafa is always fighting really hard“, Cilic said. „But I am extremely pleased with my own game.“
The world number six will now face another unexpected semi-finalist:
Kyle Edmund secured his very first spot in a Grand Slam semi-final a little bit earlier.
The 23-year-old became the only sixth British player to reach the semi-final, after Andy Murray, Tim Henman, John Lloyd, Roger Tylor and Greg Rusedski.
Murray, who had to withdraw from this year's Australian Open, twittered:
Tim Henman, one of the greatest in British tennis, was watching Edmund at Rod Laver Arena.
"I know what it feels like to be Andy Murray for the last eight years or however long. Yeah, of course, it comes with the territory of playing the sport. The better you do, the more attention you get", Edmund said.
"It's probably the first time I've done well probably, you know, on my own."
But we also saw a rather unexpected winner in the first women´s quarterfinal:
Earlier in the day, world number four, Elina Svitolina, was shocked by number 36, Elise Mertens.
“I have no words. I don’t know what to say,” the Belgian said after her win in straight sets.
“I have so many mixed emotions. I gave it all today, I fought. I got a little stress at the end so I played, my game and it went well today.
The 22-year-old world number 36 is the first Belgian to reach a Grand Slam semi-final since Kirsten Flipkens at Wimbledon four years ago.
Mertens, who had also beaten Australia´s Daria Gavrilova, took out her maiden title in Hobart last year.
Interestingly, in 2017, Elise Mertens and Sachia Vickery both claimed to suffer injuries at the same time at the Hobar tournament. Reportedly, both with an intention to play qualifiers in Melbourne later in the week.
The umpire deemed Vickery to have retired first, so Mertens advanced. The Belgian, who trains at the Kim Clijsters academy, then won the tournament and gained entry into the main draw of the French Open, where she reached the third round.
Kim Clijsters, the 2011 champion, is still in constant touch with Mertens.
She will now face Caroline Wozniacki. The world number two defeated Carla Suarez Navarro in three sets.