TennisMELBOURNE, Jan 24 Karen Khachanov reached the Australian Open semi-finals for the first time on Tuesday after Sebastian Korda retired injured while trailing 7-6(5) 6-3 3-0, dashing the American's hopes of emulating his father Petr's 1998 Melbourne Park triumph.Korda, the 29th seed, struggled with a right wrist issue that needed treatment twice during the match on Rod Laver Arena before throwing in the towel in the third set.Khachanov had also reached the last four of the 2022 U.S. Open and said it felt great to be back in a Grand Slam semi-final."Obviously not the way you want to finish a match," said the 18th seed, who will meet either third seed Stefanos Tsitsipas or unheralded Czech Jiri Lehecka for a place in the final."I think until a certain point, it was very competitive, very good battle."Sebastian beat one of my friends Daniil Medvedev in three sets and in Hubert Hurkacz in five sets I guess, he was playing great tennis."I'm feeling really good, to be honest, really happy with my level and how I compete and I'm looking forward to the semi-finals here in Australia the first time."Wimbledon champion Elena Rybakina also booked her place in the Melbourne Park semi-finals for the first time, the Kazakh 22nd seed beating Jelena Ostapenko 6-2 6-4 in a match that was played under the roof after a rain shower halted play."I'm super happy to be in the semi-finals for the first time," said Rybakina. "Of course, I was nervous, particularly in the last game, but I'm happy I managed my emotions. I played really well today."Having begun her campaign on one of the outer courts at this year's championship, Rybakina was every bit the star on the main showcourt with a dominant display in which she sent down 11 aces to quell 2017 Roland Garros champion Ostapenko.Rybakina will take on third seed Jessica Pegula or twice Australian Open champion Victoria Azarenka next."For sure, I'm going to watch it," Rybakina said of that quarter-final. "But at the same time, I need to forget about tennis for a few hours, to rest the mind, then prepare for another tough match."