All four seeds in the top half of the BMW Open draw were beaten in straight sets on a day of shocks in Munich.

Top seed Gael Monfils was thumped 6-2 6-4 by rising star Hyeon Chung while three-time reigning champion Philipp Kohlschreiber, Fabio Fognini and Mischa Zverev suffered respective losses to Guido Pella, Horacio Zeballos and Martin Klizan.

Germans Alexander Zverev and Jan-Lennard Struff, who meet on Friday, and Roberto Bautista Agut are now the only seeds remaining in the ATP 250 clay-court event, 

At the Estoril Open, the last remaining home hopes exited on Thursday as David Ferrer and Gilles Muller eased into the quarter-finals.

Veteran Spaniard Ferrer and Luxembourg's Muller each made light work of Portuguese wildcards to continue their progress.

Ferrer was a 6-3 6-4 victor over Frederico Ferreira Silva and Muller beat Pedro Sousa 6-3 6-2. Taro Daniel won the day's other match in straight sets against Bjorn Fratangelo.

There was plenty of Serbian success in Turkey meanwhile, as fifth seed Viktor Troicki, Dusan Lajovic and Laslo Djere reached the last eight of the Istanbul Open.

Troicki and Lajovic beat Russian opposition in the form of Karen Khachanov and Mikhail Youzhny. Djere shocked fourth seed Paolo Lorenzi with a 6-4 6-3 triumph.

Djere wil now take on Troicki in the quarter-finals, while Lajovic is set to face Diego Schwartzman, a straight-sets winner over Jordan Thompson.