Top seed Stan Wawrinka exits Swiss Indoors after loss to qualifier Mischa Zverev

The three-time grand slam champion experienced difficulties when dropping a set in a previous round against another wildcard, Marco Chiudinelli, and Zverev broke Wawrinka six times in winning 6-2 5-7 6-1.

It was the first time in six years the German had recorded a victory over a top-10 ranked opponent and his reward, as well as a spot in next week's Paris Masters main draw, is a semi-final meeting with Marin Cilic, who defeated Marcel Granollers 6-3 6-3.

The highest seed remaining in the tournament is Kei Nishikori as he claimed his 55th win on the tour this year, and his first ever over Juan Martin del Potro.

The Argentinian had not dropped a set to Nishikori in their previous four meetings but the world number five claimed a solitary break in either set to advance courtesy of a 7-5 6-4 victory.

At the Erste Bank Open in Vienna, defending champion David Ferrer kept alive his chances of retaining his title with a gutsy three-set win over Viktor Troicki.

Ferrer won the first set but was pegged back in the second and three unforced errors saw Troicki take an early break at the beginning of the third.

Troicki was then serving for the match at 5-4 but Ferrer fought back and eventually converted a match point at the fourth time of asking to claim a 6-3 3-6 7-5 success.

He will meet world number two Andy Murray in the semi-final, with Jo-Wilfried Tsonga facing Ivo Karlovic in the other last-four tie after they both won on Friday.

Frenchman Tsogna was a 6-2 7-6 (7/5) victor over Albert Ramos-Vinolas while Karlovic defeated wildcard Karen Khachanov 6-7 (5/7) 7-6 (7/5) 6-3.