Greek third seed Stefanos Tsitsipas battled back from a set down to beat Serbia's Filip Krajinovic 3-6 6-4 6-4 in the quarter-finals of the Swiss Indoor championship on Friday.
The win took Tsitsipas into his 10th semi-final of the season where he will face top seed Roger Federer, who was handed a walkover after Swiss compatriot Stan Wawrinka withdrew before their quarter-final with a back issue.
Federer is looking to win his 10th title in Basel and his third in a row for a second time after a hat-trick of titles from 2006-2008.
Tsitsipas fired 12 aces and 38 winners in a match where both players dropped serve three times, but the Greek 21-year-old was far more effective on his second serve.
It was the 11th time this season that he had come back from a set down to win a match.
The other semi-final is between unseeded pair Alex de Minaur of Australia and American Reilly Opelka.
Wildcard De Minaur won 6-4 7-6(4) against Germany's Jan-Lennard Struff while big-serving Opelka sent down 31 aces as he beat Spanish fourth seed Roberto Bautista Agut 6-3 3-6 6-3.
