Marius Copil on Saturday became the first qualifier to reach the final of the Swiss Indoors in more than a decade as the Romanian upset Alexander Zverev 6-3, 6-7 (6/8), 6-4.
The world number 93, the first player from qualifying to go this far here since Marcos Baghdatis in 2005, will face the winner from eight-time champion Roger Federer and Russian Daniil Medvedev.
Copil will be playing the biggest match of his career after overcoming second seed Zverev, with the Romanian having dropped just one set in six matches in Basel.
The 28-year-old outsider fired 26 aces, with his impenetrable service game laying the basis for a surprise win.
He needed 44 minutes to claim the opening set but was brought back to level-pegging as Zverev won the second in a tiebreaker.
In the third, Copil kept pace, with Zverev faltering on serve in the 10th game and his opponent taking advantage with a cross-court volley winner to advance amid cheers for the underdog.
Copil stands 2-0 over potential opponent Medvedev but has never played Federer.
The Romanian had already upset 2016 champion and third seed Marin Cilic in the second round.