Pablo Andujar broke Swiss hearts for the second time this week in Geneva, having first downed veteran Roger Federer and then teenage starlet Dominic Stricker in Thursday's quarter-finals.
The Spaniard wrecked 39-year-old Federer's first match for two months in Tuesday's round of 16, and the in-form clay-court specialist then sunk 18-year-old Stricker to reach Friday's semis.
The world number 75 beat the 2020 French Open boys' champion 4-6, 6-4, 6-4 after Stricker became the youngest player from his country to reach an ATP quarter-final since Federer at Copenhagen in 2000.
Stricker, the world number 419, stunned 2014 US Open champion Marin Cilic in his first-ever match on the main tour, then downed 2018 Geneva title winner Marton Fucsovics.
But 35-year-old Andujar had the better of him.
"It's very difficult when you're facing Roger and for sure, it's very difficult when you're facing a young guy who is very talented and has nothing to lose," the Spaniard said.
"You are never calm, never relaxed because he's always trying to attack.
"I think he's going to improve; I'm sure he will. I really think he's going to be a very, very good player."
Overall, Stricker was delighted with his main tour debut.
"It was a great week for me. I won against two top-50 players which is just amazing to know that I am actually on this level and I can compete against these guys," he said.
At 18, Stricker is now too old to defend his French Open junior title - and was not among the wildcards for the Roland Garros main draw.
Instead of heading for the Grand Slam event in Paris, which starts on 30 May, he will find himself back at the grindstone in an a third-tier tournament in Kiseljak in Bosnia next week.
Asked if he would like to be back on the main ATP tour again soon, Stricker said: "I hope so, yes. We will have to see."
Andujar will face Norwegian rising star Casper Ruud in Friday's semi-finals.
The 22-year-old third seed battled back from behind to beat Germany's Dominik Koepfer 2-6, 6-1, 6-4.
Ruud has been one of the impressive clay-court performers in recent months, making the semi-finals at Monte Carlo, Munich, Madrid and now Geneva.
"It will be a new challenge but the body is feeling good. I have played two matches without any pain and that's a nice sign. The body feels ready," Ruud said ahead of his semi-final with Andujar.
Uruguayan qualifier Pablo Cuevas won two matches in a day at the Eaux-Vives club to book his spot in the semi-finals.
The 35-year-old clay-courter beat teenage French qualifier Arthur Cazaux 6-2, 6-4 in the afternoon then came back in the evening to down Bulgarian fourth seed Grigor Dimitrov, the world number 20, 7-6 (7/3), 6-3.
Cuevas, ranked 102, will face either Canadian second seed Denis Shapovalov or Serbia's Laslo Djere in Friday's last four.