No. 5 seed Nishikori defeated Thiem 6-3, 6-1 in Vienna to advance to the semifinals, where he will face Mikhail Kukushkin. With his victory Friday, Japan's Nishikori moved above John Isner into ninth in the ATP Road to London standings -- one spot below Thiem.
"I'm just happy to play good tennis," Nishikori told the ATP Tour's official website. "Hopefully I can make London, but there is still one more tournament next week in Paris, so I just play 100 percent here in Vienna and hope I can carry on the momentum to Paris."
No. 2 seed Kevin Anderson moved into the final four after opponent Borna Coric retired injured with the match at 7-6 (2), 1-2 in the South African's favour. He will face Spaniard Fernando Verdasco, who was up 6-4, 2-1 against Gael Monfils before the Frenchman also retired.
Earlier, qualifier Kukushkin came from a set down to beat Marton Fucsovics 4-6, 7-6 (2), 7-6 (4).