Karen Khachanov reached the quarterfinals of the US Open for the first time on Sunday after upsetting Spanish 12th seed Pablo Carreno Busta in a five-set thriller.
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The 27th seed from Russia set up a last-eight meeting against either defending champion Daniil Medvedev or Australia's Nick Kyrgios after prevailing 4-6, 6-3, 6-1, 4-6, 6-3 on the Louis Armstrong Stadium.
The result equals Khachanov's best ever result in a Grand Slam tournament.
The 26-year-old from Moscow reached the quarterfinals at Wimbledon in 2021 and the French Open in 2019, but had never gone further than the third round in New York.
Khachanov said after the gruelling 3hr 21min duel he had taken confidence from the fact he had won his last three encounters with Carreno Busta.
"We always have unbelievably tough matches, so I was prepared physically to just play my best," the Russian said.
"I won the last three matches against Pablo and that gave me confidence from the beginning."