Astana, Kazakhstan — Novak Djokovic dominated Russian Karen Khachanov 6-4, 6-3 to reach the Astana ATP semi-finals on Friday where he will face Daniil Medvedev.

"I didn't play as well from the baseline as I did in the first two matches, but still it was enough," said Djokovic.

"I managed to produce some good tennis when it was the most needed in both sets."

Facing the US Open semi-finalist, the Serb dropped serve for the first time this week but still has not lost a set since returning to the ATP Tour after a three-month break following his Wimbledon title.

He made his comeback at the Laver Cup team event in London before winning the Tel Aviv tournament last weekend for his 89th career crown.

In the semi-finals, Djokovic will face world number four Medvedev, the man who ended his bid for a calendar Grand Slam in 2021 by winning the US Open.

"I always expect highs from myself," said 21-time Grand Slam title winner Djokovic.

"Hopefully I can elevate still the level of my game for tomorrow because it's going to be needed."

Medvedev made the last-four by seeing off Roberto Bautista Agut of Spain 6-1, 6-1 to record his 40th win of 2022.

Second seed Medvedev trails Djokovic 6-4 in career meetings.

"I am really happy to play against Novak," Medvedev said.

"I thought about it before the match and we have only played one tournament together this year, which was Roland Garros. This is the second one and we meet again and I am really happy."

In Saturday's other semi-finals, Andrey Rublev, the fifth seed from Russia, will tackle Greek third seed Stefanos Tsitsipas.

On Friday, Rublev defeated Adrian Mannarino 6-1, 6-2 while Tsitsipas saw off Hubert Hurkacz 7-6 (10/8), 6-3.

Meantime, Nick Kyrgios withdrew from the Japan Open just minutes before his quarter-final on Friday with a sore left knee, calling it "heartbreaking".

The mercurial Australian star had been scheduled to play third-seeded American Taylor Fritz, who will now play Canada's Denis Shapovalov, seeded seventh, in the last four on Saturday.

At a hastily announced press conference when the match was due to begin, world number 20 Kyrgios said he had "been playing amazing tennis all year" but it had been physically taxing.

"I actually was dealing with a bit of a knee issue around the US Open time, and got back home, probably didn't take enough time off, to be honest. I went straight back into training," said the 27-year-old.

"It's heartbreaking. When the body lets you down, it's not a good feeling."

Kyrgios will now head home, but said he still plans to play several events in the run-up to the Australian Open in January, and promised to return to the Japanese tournament in 2023.

Kyrgios, who on Thursday beat Poland's Kamil Majchrzak 3-6, 6-2, 6-2 in the second round, said his knee had "not really" been an issue in his singles or doubles matches, but it had felt "pretty sore" while warming up on Friday.

"It's probably in this case something overloading, rather than not being fit enough," he explained.

"It's almost being too excited to get on the court, and maybe training a little bit too much."

Earlier on Friday, a jet-lagged Frances Tiafoe flew into the semi-finals in straight sets, clinching each with an ace to beat Serbia's Miomir Kecmanovic 6-0, 6-4.

The fourth-seeded US player will face unseeded Kwon Soon-woo of South Korea on Saturday.

Tiafoe, who beat Rafael Nadal at the US Open on the way to his first Grand Slam semi-final, said he had been "solid from the start" of the 71-minute quarter-final.

"Great tennis today," he said. "I was moving really well, I hit the ball really well from the back of the court."

The 24-year-old American, the world number 19, said he had been struggling to adapt to the Tokyo time zone.

"I've been really bad and jet-lagged, so I've probably been sleeping pretty early and waking up really early," he said.

Canada's Shapovalov won a place in the semi-final with a 6-4, 6-3 victory over Croatian Borna Coric, while Kwon beat Spain's Pedro Martinez 6-3, 6-0.

Tiafoe said it would be "cool" to play the South Korean, who he faced at the Tokyo Olympics.

"Kwon's a great player. He's been playing really well this week, so it's going to be cool to play him, we practice sometimes in Florida."