Australian, Nick Kyrgios is out of the US Open after eventually being out-battled by Russia's Karen Khachanov in a tense quarter-final in New York.

The 27-year-old Australian, who needed treatment on his left thigh after the first set, lost 7-5 4-6 7-5 6-7 (3-7) 6-4 to 27th seed Khachanov.

"I feel like I've let so many people down," said Kyrgios.

The world number 31 edged a tight opener when the first break point of the match went his way in the 12th game, with Kyrgios requiring treatment afterwards and saying he was struggling to walk.

But Kyrgios recovered and found top gear in the second set to level the match.

The Wimbledon runner-up continued to create chances in the third set, but grew frustrated when his forehand broke down in the ninth game and stopped him taking any of two break points.

After clattering his racquet on the court, Kyrgios was unable to forget the missed opportunities as he served.

He survived two set points in the 10th game - the first when Khachanov inexplicably whacked a poor drop-shot into the stands - but could not see off another in the 12th after the Russian's relentless returning continued to draw out errors.

Khachanov, 26, plays Norwegian fifth seed Casper Ruud, who beat 13th seed Matteo Berrettini 6-1 6-4 7-6 (7-4).