Rafael Nadal's path to an 11th Barcelona title was cleared of dangermen Grigor Dimitrov and Dominic Thiem on Friday when they crashed to shock quarter-final losses.
Second seed Dimitrov was knocked out by fifth-seeded Spaniard Pablo Carreno-Busta 6-3, 7-6 (7/4).
Thiem, the third-seeded Austrian, was stunned by 19-year-old Stefanos Tsitsipas with the fast-rising Greek stunning the world number seven 6-3, 6-2 in 80 minutes.
World number 63 Tsitsipas won the last 14 points of the match to reach the semi-finals.
It was his second win over a top 10 player following his victory over Belgium's David Goffin in Antwerp last October.
He will face Carreno-Busta for a place in the final.
Nadal, who has won his last 40 sets played on clay, was taking on Slovakian qualifier Martin Klizan for a place in the semi-finals.
Klizan, ranked at 140, had defeated Novak Djokovic in the second round.
The day's other quarter-final sees Goffin, the fourth seed, facing Roberto Bautista Agut, the eighth-seeded Spaniard.