World number 137 Jiri Lehecka of the Czech Republic reached his maiden ATP semi-final in Rotterdam on Friday where he will face top seed Stefanos Tsitsipas.
Lehecka, a 20-year-old qualifier, defeated Italy's Lorenzo Musetti 6-3, 1-6, 7-5 in his quarter-final clash.
"It is an incredible feeling. The things I am achieving here are incredible. This is the big stage and I am happy I can be here and play these matches," he said.
"Today it was another tough match against an incredibly tough opponent. I will now try and rest ahead of tomorrow and we will see."
He is the lowest-ranked Rotterdam semi-finalist since world number 225 Omar Camporese reached the last four in 1995.
World number four Tsitsipas eased past Alex de Minaur of Australia 6-4, 6-4 in his last-eight match.
"Lehecka has been on a very good winning streak," said Tsitsipas.
"I think he's a young talent that can play really good tennis. It's never easy playing someone who you haven't faced before, so match preparation will be very important."
Third seed Felix Auger-Aliassime also made the last-four with a 7-5, 7-6 (7/4) win over Cameron Norrie.
It was the Canadian's second successive victory over a British player having knocked out former world number one Andy Murray on Wednesday.
He next faces Russian second seed and defending champion Andrey Rublev who defeated Marton Fucsovics of Hungary 6-4, 6-3.
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