Basel - Australia's Alex de Minaur survived a barrage of 26 aces from American giant Reilly Opelka to battle to a 7-6 (7/2), 6-7 (4/7), 7-6 (7/3) win in the Swiss Indoors semi-finals on Saturday.
The 20-year-old, who trains and lives in Spain, will target his fourth title of 2019 on Sunday when he faces either nine-time champion Roger Federer or third seed Stefanos Tsitsipas.
The world No 28 is the first Australian to reach the Basel final since Mark Philippoussis finished runner-up in 1997
De Minaur, who measures up at 1.80m compared to Opelka's towering 2.11m, set up victory with a passing winner for four match points.
Opelka saved the first with an ace but was caught out on the second as his opponent sealed the win.
"Nothing can prepare you for that serve," De Minaur said. "Reilly's an incredibly tough competitor who never gives up.
"I'm just happy to be in the final. I guessed right a few times and got lucky. I was just lucky to have gone the right direction, I was just hoping not be hit by any of those serves.
"I felt comfortable out there, my reflexes are better if I stand closer on return. You can't give him too many angles to work with."
De Minaur has won all three of his finals this season at Sydney, Atlanta and Zhuhai.
Results from the ATP tournament in Basel on Saturday (x denotes seeding):
Alex De Minaur (AUS) bt Reilly Opelka (USA) 7-6 (7/2), 6-7 (4/7), 7-6 (7/3)
Roger Federer (SUI x1) v Stefanos Tsitsipas (GRE x3)