Basel - Canadian rising star Denis Shapovalov fought hard to beat Japan's Yuichi Sugita 4-6, 6-2, 7-6 (7/3) in the first round of the Swiss Indoors on Monday.
The 18-year-old, ranked a career-high 49th in the world and making his Basel debut, continued his breakthrough season by qualifying for next month's ATP NextGen Finals.
Shapovalov will next face either Belgian Ruben Bemelmans or seventh seed Adrian Mannarino of France.
The Canadian made his entrance on the big stage in August with a win over Rafael Nadal on home soil in Montreal, before a run to the US Open last 16 at Flushing Meadows.
On Monday, he became the fourth player to book a spot for the inaugural ATP NextGen Finals in Milan, joining German Alexander Zverev and Russians Andrey Rublev and Karen Khachanov.
Shapovalov started slowly against Sugita, a Cincinnati quarterfinalist two months ago, dropping the opening set.
In the second, the left-hander earned an early break and finished with another, after Sugita saved one set point with an ace but drove a forehand into the net on Shapovalov's second chance.
The charismatic youngster moved into a 3-1 lead in the final set, before being broken in the seventh game.
But Shapovalov took a 5-3 lead in a deciding tie-break and smashed an overhead winner to bring up three match points, before Sugita double-faulted on the first.
"It was a battle, I had to fight to stay in it," Shapovalov said. "I have to lift my game for the next round."
Spanish sixth seed Roberto Bautista Agut eased past Kazakhstan's Mikhail Kukushkin 6-0, 6-3.
The Basel field is headed by seven-time champion Roger Federer, who has played 12 finals in his hometown and is making his 17th main-draw appearance at the St Jakobshalle.
The home favourite earned his first ATP qualifying win at the site 20 years ago aged 17, and will be looking for a seventh title of the year in his bid to unseat Nadal as world number one.
Defending champion Marin Cilic is seeded second as the Croatian fights for a place in the ATP Finals at London next month.
Former US Open winner Juan Martin Del Potro is the fourth seed ahead of Belgian David Goffin.
Results from the Swiss Indoors tournament in Basel on Monday (x denotes seeding):
Denis Shapovalov (CAN) bt Yuichi Sugita (JPN) 4-6, 6-2, 7-6 (7/3)
Hyeon Chung (KOR) bt Paolo Lorenzi (ITA) 6-3, 6-1
Robin Haase (NED) bt Marco Chiudinelli (SUI) 6-2, 7-6 (7/3)
Roberto Bautista Agut (ESP x6) bt Mikhail Kukushkin (KAZ) 6-0, 6-3