Nick Kyrgios roared back from a "frustrating" first set on Thursday to reach the quarter-finals of the Japan Open, defeating Polish player Kamil Majchrzak 3-6, 6-2, 6-2.

Despite his slow start, the maverick Australian emerged victorious in typical crowd-pleasing style, showing off with aggressive aces and some exaggeratedly effortless points.

The 27-year-old, who was knocked out in the last eight at the US Open, said that despite Majchrzak breaking his serve, there was "never really doubt in my mind that I was going to win".

"I've barely been broken all year," so when "the opponent doesn't really do much to break me it's quite frustrating," he said after the 1h 21min match.

"I was just not playing the right way -- the court's very fast," Kyrgios added.

But by being "a bit more aggressive" in the second and third sets, the world number 20 said he "ended up just weathering the storm and then coming through".

"I've got really good confidence in my game right now. So I don't really doubt myself, even when I'm down a set... firing Grand Slams has given me that confidence."

Kyrgios, whose lawyer appeared for him at a court hearing in Australia this week for a charge of common assault, will face either third-seeded US player Taylor Fritz or Japan's Hiroki Moriya in the quarter-finals.

Fritz has had a "breakthrough year", fifth-seeded Kyrgios said, while the crowd in Tokyo is bound to get behind home favourite Moriya.

"Either way, it's going to be a tough match."

- 'I wanna win for me' -

Earlier in the day, Frances Tiafoe came through a second set battle to secure a spot in the quarter-finals, saying he wasn't bothered by rising expectations.

The 24-year-old American, who has been in the spotlight since beating Rafael Nadal on the way to a first Grand Slam semi-final at the US Open last month, beat Spaniard Bernabe Zapata Miralles 6-1, 7-6 (9/7).

The American breezed through the first set before Miralles fought back to take the second to a tie-break that saw some of the best rallies of the 1hr 32min encounter.

"Good match today, tough second set," said Tiafoe, who has won his last 13 tie-breaks.

"Sometimes it tips well your way. I'm playing very aggressive, I'm serving well in the tie-breaks, always a couple of aces."

He will face Miomir Kecmanovic in the last eight, after the Serb beat Britain's Dan Evans 6-3, 3-6, 7-6 (7/4).

After stunning Nadal at Flushing Meadows, Tiafoe played a starring role at the Laver Cup in London where his Rest of the World Team beat Europe for the first time in the competition's history.

But the fourth-seeded player, currently world number 19, said he was comfortable with all the attention he is receiving.

"I don't really care about what other people think I should be doing because I've had recent success.

"You know: 'Oh, is he going to be the next...?'," he said.

"I've been on tour for seven or eight years now, none of that really moves me. I wanna win for me, I'm not trying to achieve anybody else's goals."