Milestone win for Del Potro
Defending champion Juan Martin del Potro progressed to the semi-finals of the Swiss Indoors thanks to his 300th career victory.
Del Potro was a 6-4 6-4 winner against France's Paul-Henri Mathieu to reach the milestone.
He broke Mathieu's serve once in each set and did not face even a break point on his own delivery while sending down 11 aces.
Del Potro will take on another Frenchman, Edouard Roger-Vasselin, in the last four. Roger-Vasselin saw off Germany's Daniel Brands 6-3 4-6 6-3.
"I played a good match," said Del Potro. "I was solid from the baseline and served well.
"I've been working a lot of my serve. I'm playing better and better with each match.
"I'm looking forward to tomorrow and I'll have to lift my level even more."
Local hero Roger Federer will take on Canadian Vasek Pospisil in the other semi-final.
Federer, who was denied a sixth title at his home event by Del Potro in last year's final, earned a 6-3 7-6 (7/2) victory against eighth seed Grigor Dimitrov in the final match of the day.
Pospisil defied a stiff neck to defeat Ivan Dodig of Croatia 7-6 (13/11) 6-4 in his quarter-final.