Stefanos Tsitsipas set up his fourth meeting this season with Roger Federer after a 3-6 6-4 6-4 quarter-final comeback win over Filip Krajinovic at the Swiss Indoors on Friday.
The Greek world number seven has beaten nine-time Basel champion Federer at the Australian Open while benefitting from a walkover on the clay in Rome. In between, Federer, 38, swept past the 21-year-old Greek in Dubai.
Top seed Federer on Thursday had already made sure of his spot in the semi-finals after Swiss compatriot Stan Wawrinka withdrew from their last-eight tie with a lower back injury just an hour after seeing off Frances Tiafoe in a gruelling second round clash.
On Friday, Tsitsipas had to stage a fightback for a second straight match after recovering against qualifier Ricardas Berankis 24 hours earlier.
"Persistence was the key today," said third seed Tsitsipas. "I put a lot of emphasis on my serve. It was also crucial to stay concentrated, even if I was broken three times, unfortunately. But there were plenty of games where I played very confidently."
"It was one of the greatest moments of my career. Of course, the crowds love Roger -- but what can you do?