Italian 19-year-old Jannik Sinner became the Barcelona Open's youngest semi-finalist since 2005 after overcoming Russian Andrey Rublev 6-2, 7-6 (8/6) on Friday.
Sinner, ranked 19th in the world, will next face Stefanos Tsitsipas after the Greek second seed defeated Felix Auger-Aliassime 6-3, 6-3.
"I am trying to get better every week," Sinner said.
"He (Rublev) has played many, many matches already this year and I tried to play my tennis.
"It was difficult to finish it off. I had three break points at 5-5 (in the second set), which I could not convert, but I'm pleased to win in the end," he added.
Rafael Nadal, who has won 20 Grand Slam singles titles, reached the Barcelona last four as an 18-year-old 16 years ago.
Nadal faces Britain's Cameron Norrie later for a place in the semis as he seeks a 12th title in Barcelona.