Nick Kyrgios knocked out of US Open after 'terrible' early drama

Nick Kyrgios has been knocked out of the US Open after an epic five-set thriller against Karen Khachanov after the Aussie star appeared to be on the verge of retiring hurt during the early stages of the match.

Kyrgios staged a fightback after appearing close to retirement with a leg injury, but wasn't able to overcome Khachanov, who won 7-5 4-6 7-5 6-7 6-4.

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The Australian was left fuming after the match and smashed his racquet, before swiftly exiting court.

The match started with both Kyrgios and Khachanov powering through the opening set at Arthur Ashe Stadium on Tuesday night, with the Russian taking it 7-5 in just 35 minutes.

Kyrgios was barely moving during rallies as he appeared to be hampered by a lower leg injury, and called for the trainer at the end of the set.

The Aussie star could be seen telling his player's box that his knee was troubling him and that he couldn't walk properly, before the trainer proceeded to work on Kyrgios for an extended period.

Kyrgios was trying to keep rallies short so he didn't have to do too much running, and was a virtual passenger during Khachanov's service games.

At one stage the Russian produced a rare 'golden game' in which he reeled off four consecutive aces, with a helpless Kyrgios simply watching on in vain.

Early in the second set Kyrgios could be heard telling his entourage "I don't want to f***ing play through this sh*t", suggesting he was considering retiring hurt.

Fans were left gutted for Kyrgios despite the fact he managed to play on, with the Aussie coming into the clash on the back of 20 wins in his last 23 singles matches.

Some suggested the Aussie star shouldn't have been playing doubles so deep into the tournament after his loss alongside Thanasi Kokkinakis on Monday.

But in remarkable scenes, Kyrgios managed to battle through the injury to claim the second set 6-4, moving much more freely to level the match.

The Aussie star looked a completely different player as he worked his way back, but dropped his serve at the worst possible time to lose the third set 7-5.

Kyrgios smashed his racquet and raged at his box as frustration started to set in.

He recovered to win the fourth set in a tie-breaker. but was broken early in the fifth.

The Australian battled to remain in the match, but some power-hitting from Khachanov saw the Russian advance to his first ever US Open semi-final.

Casper Ruud advances to US Open semi-finals

Khachanov will face Casper Ruud in the semi-finals after the Norwegian fifth seed beat Matteo Berrettini 6-1 6-4 7-6 (7-4).

Ruud must at least reach the final to have a chance at ending the US Open as the top-ranked player in the world - a chance he gets thanks to Kyrgios' fourth-round defeat of current No.1 Daniil Medvedev.

Rising Spanish star Carlos Alcaraz and Rafael Nadal, who lost on Monday, can also both end the year's final grand slam event as the new top-ranked player

"Of course it's a little bit (more) motivation," said Ruud. "I'm trying to go for it, of course."

Earlier, Ajla Tomljanovic's inspired US Open run was ended in a hard-fought quarter-final loss to Ons Jabeur.

Runner-up at Wimbledon, Jabeur delivered a centre-court masterclass to subdue Tomljanovic 6-4 7-6 (7-4) in a high-quality encounter.

The first Australian to make the women's last eight at Flushing Meadows since former champion Sam Stosur a decade ago, Tomljanovic threw everything at Jabeur and went down swinging.

"I knew physically it was going to be a tough match," Jabeur said.

"Even emotionally, it was tough to manage the frustrations because when you have breaks, you want to finish.

"But she keeps fighting and makes it tough for me.

"I'm just here trying to do my job and hopefully I can inspire more and more generations from Africa. It really means a lot to me."

Jabeur will play Caroline Garcia in the semis after the French player beat Coco Gauff 6-3 6-4.

with AAP

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