Aussie firebrand Kyrgios stunned by Khachanov in US Open quarter-finals

Russia's Karen Khachanov reached his first Grand Slam semi-final at the US Open on Tuesday with a 7-5, 4-6, 7-5, 6-7 (3/7), 6-4 win over Australian firebrand Nick Kyrgios.

Khachanov, seeded 27, fired 30 aces and a total of 63 winners past Wimbledon runner-up Kyrgios in a big-serving contest.

The 26-year-old will face fifth seed Casper Ruud of Norway for a place in Sunday's final.

"I did it, guys. Finally, you are showing me some love," Khachanov told the mostly pro-Kyrgios crowd on Arthur Ashe Stadium.

"It was a crazy match I was expecting it would be like this. I'm ready to run, to fight to play five sets. We played almost four hours and that's the only way to beat Nick."

The Russian said he had "nothing to lose" when he faces French Open runner-up Ruud on Friday.

"I would like to win it," he said.

"But as deep as you go the expectations rise up. I did the step forward, I made my first semi-final and I think I have nothing to lose.

"I just want to go for it and be ready for the next match and hopefully it will be a good one."

That semifinal feeling.@karenkhachanov fights past Nick Kyrgios in five intense sets. pic.twitter.com/c0vfZ5XbNf

Kyrgios was feeling his left knee at each changeover in the first set on Tuesday and summoned the trainer after dropping the opener complaining 'I can't walk'.

It was a rapid-fire first set dominated by serve with Khachanov sending down four successive aces to lead 6-5 before pouncing on the only break point to seal the set.

Despite his physical worries, the 27-year-old Kyrgios, who knocked out defending champion Daniil Medvedev in the fourth round, broke for 2-1 on his way to pocketing the second set.

Kyrgios served up a 47-second service game, courtesy of four aces in a row, but wasted two break