Kei Nishikori is two wins away from defending his title at the Barcelona Open after claiming his place in the final four.
Gilles Simon's bid for a fourth title in Bucharest came crashing down after being beaten by Spain's Daniel Gimeno-Traver.
Simona Halep continued her winning habit in 2015 as she saw off Sara Errani to reach the semi-finals in Stuttgart.
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Three-time defending champion Maria Sharapova was knocked out of the 2015 Porsche Tennis Grand Prix on Thursday.
Rafael Nadal's bid for a ninth Barcelona Open title ended in third-round defeat at the hands of Italy's Fabio Fognini.
Agnieszka Radwanska became the second high-profile exit in Stuttgart in as many days after losing out to Sara Errani.
Rafael Nadal avenged last year's loss to Nicolas Almagro by beating his fellow Spaniard 6-3 6-1 at the Barcelona Open.
Lukas Rosol kept up his quest to reach a third successive final at the BRD Nastase Tiriac Trophy in Bucharest.
Kei Nishikori made a winning start to his Barcelona Open title defence with a straight-sets victory over Teymuraz Gabashvili.