Top seed Croatian Marin Cilic was swept out of the Memphis International tennis tournament, falling 6-4 6-2 to Japan's Kei Nishikori on Friday.
Cilic blasted 12 aces past his fifth seeded opponent but converted only one of two break points in the 72-minute quarter-final loss.
"It's getting better every match ... little by little," world number 22 Nishikori told reporters when asked about his game.
"I was dominating with my serve."
Nishikori, who became the first Japanese player into the Memphis semi-finals since the tournament's inception in 1976, will meet Marinko Matosevic on Saturday after the Australian pulled off another upset by outlasting seventh-seeded Ukrainian Alexandr Dolgopolov 6-7 6-2 6-4.
Spain's Feliciano Lopez will play Uzbek Denis Istomin in the other semi-final.
Lopez ended American wild card Jack Sock's run 6-4 6-3 in 82 minutes, collecting seven aces and saving four of five break points, while Istomin eliminated American Michael Russell 6-4 7-6.
Repeat finalist Marina Erakovic of New Zealand will face Germany's Sabine Lisicki for the women's title.
Erakovic defeated Stefanie Voegele of Switzerland 6-2 6-4. Lisicki beat Magdalena Rybarikova of Slovakia 7-5 7-5.
(Reporting by Steve Keating in Toronto and Gene Cherry in Raleigh, North Carolina; Editing by Ian Ransom)