Spain's Marin, the number one seed for the women's singles, triumphed 21-17, 17-21, 21-13 in 64 minutes over seventh seed Sayaka Sato of Japan at the Innogy Sporthalle.

Unseeded Minatsu Mitani overcame eighth seeded Japanese compatriot 10-21, 21-18, 21-5 in other women's singles quarter-final matches.

China's Chen, seeded second for this week's event, won with ease in the corresponding men's event after Danish opponent Hans-Kristian Solberg Vittinghus retired when trailing 21-10, 5-3.

Sixth seed Chou Tien Chen was among others to progress.

The Taiwanese player won 21-10, 21-14 over another Danish player in Emil Holst. 

It came on a good day for Taiwan as Tzu Wei Wang also overcame Zvonimir Durkinjak of Croatia, 21-19, 21-9.

Japan's Takuma Ueda completed the semi-final line-up by beating Ng Ka Long Angus of Hong Kong 14-21, 21-17, 21-15.

Last four matches are due to take place tomorrow before finals on Sunday (March 5).