Kei Nishikori ended Juan Martin del Potro's long winning run at the Swiss Indoors, edging their quarterfinal 7-5, 6-4 on Friday.
The third-seeded Japanese saved all eight of Del Potro's break-point chances, and created match point with his seventh ace. Nishikori clinched with an overhead volley winner at the net.
"I saved a lot of important points with my serve," said Nishikori, who had 10 break chances and took one in each set. "I played good tactics today."
Del Potro, a wild-card entry here, won back-to-back Basel titles in 2012 and 2013. The 28-year-old Argentine missed the next two editions due to persistent left wrist injuries.
In Saturday's semifinals, Nishikori plays Gilles Muller of Luxembourg, who earlier outlasted Federico Delbonis of Argentina 6-7 (4), 6-4, 7-6 (3).