Carlos Alcaraz disarmed Alex de Minaur 7-5, 6-3 and will face Arthur Fils for the second straight week with a trip to the Barcelona final on the line.
Zverev reaches the semis in Munich for the fourth time.
Ostapenko will put her undefeated record against Swiatek on the line on Friday.
Carlos Alcaraz and compatriot Alejandro Davidovich Fokina each scored straight sets wins to give Spain two of the last eight in Barcelona.
The two-time champion is into the quarterfinals at Stuttgart.
Ben Shelton broke three times beating Botic van de Zandschulp 7-6(1), 6-3 to reach his maiden Munich quarterfinal.
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