Unseeded duo Sorana Cirstea and Jule Niemeier marched into the semi-finals of the Internationaux de Strasbourg on Thursday.

Romanian Cirstea emphatically beat eighth seed Zhang Shuai 6-2 6-1 and moved into the last four after Bianca Andreescu withdrew following her second-round success over Maryna Zanevska due to an abdominal injury.

Cirstea lost only seven of the 31 points on her first serve and did not face a solitary break point in an impressive victory ahead of the French Open.

She broke Zhang on four occasions and will do battle with Magda Linette for a place in the final.

Linette took out fourth seed Yulia Putintseva 6-3 6-3, breaking once in the first set and three times in the second.

Qualifier Niemeier upset seventh seed Shelby Rogers, completing a 6-4 7-6 (8-6) victory following a rain delay. 

The German will look to pull off another surprise when she faces Barbora Krejcikova, who eliminated Ekaterina Alexandrova with a 7-6 (7-4) 6-1 victory.