Tokyo - Bjorn Borg lookalike Stefanos Tsitsipas survived a mid-match meltdown to beat Australia's Alex de Minaur 6-3, 5-7, 6-1 on Thursday and reach the Japan Open quarter-finals.
The 20-year-old Greek will face local hero Kei Nishikori for a place in the last four after the fifth seed came through an absorbing contest in two hours, 20 minutes.
Elsewhere, second seed Kevin Anderson also advanced, while Germany's Jan-Lennard Struff continued his dream run in Tokyo.
Tsitsipas, ranked 15th in the world, is something of a throwback.
He bears more than a passing resemblance to tennis legend Borg - from his ice-cool demeanour down to the headband and tight shorts.
His game also relies more on angles and touch than today's power merchants, and the sweeping one-handed backhand Tsitsipas drilled past de Minaur for most of their match has all the hallmarks of his idol Roger Federer.
He reached his first two ATP finals this year, losing both times to Rafael Nadal in Barcelona and Toronto.
But Tsitsipas will feel he has the weapons to upset Nishikori, despite squandering two match points to surrender the second set.
"I expect a tough match against him," he said. "Obviously he's playing at home so he's going to be super-pumped to do well. I need to be well prepared for that battle."
Wimbledon finalist Anderson ultimately had too much in the locker for young American Frances Tiafoe, progressing with a 6-3, 3-6, 6-2 victory.
The South African, ranked ninth in the world, will face eighth seed Richard Gasquet in the last eight after the Frenchman ousted Australian Nick Kyrgios 7-6 (7/4), 7-6 (7/1).
"Kevin is a top 10 player and has been in the Wimbledon and US Open finals so I have nothing to lose," said Gasquet.
"I know what I have to do to beat him but I also know it will be very tough."
Struff, who dumped out top seed Marin Cilic in the first round, produced a gutsy 7-6 (7/3), 6-7 (2/7), 6-4 win over Frenchman Jeremy Chardy.
The world number 56 next faces Denis Shapovalov after the Canadian knocked out three-time Grand Slam winner Stan Wawrinka late on Wednesday.