WASHINGTON (AP) -- Kei Nishikori withstood 15 aces and managed to break Sam Groth's big serve twice for a 6-4, 6-4 victory in the Citi Open quarterfinals Friday.
The second-seeded Nishikori, last year's runner-up at the U.S. Open, saved all four break points he faced en route to reaching a tournament's semifinals for the sixth time this season -- and first in five appearances at the hard-court event in Washington.
The first Japanese man to reach a Grand Slam final improved to 41-9 in 2015. Only Novak Djokovic and Andy Murray have won more ATP this matches this year, with 48 apiece.
Next for Nishikori could be a rematch from New York: In the semifinals, he will meet the winner of the match later Friday between reigning U.S. Open champion Marin Cilic and 18-year-old Alexander Zverev.
With both Cilic and Nishikori in Washington, this is the first time the Citi Open field included both finalists from the previous year's U.S. Open.
The men's quarterfinals on the other half of the draw scheduled for Friday night: No. 8 John Isner of the United States vs. Ricardas Berankis of Lithuania, and No. 15 Jack Sock vs. Steve Johnson in an all-American matchup.
In women's action, 2011 U.S. Open champion Sam Stosur moved into the semifinals when Monica Niculescu stopped playing because of a left abdominal strain while trailing 4-0.
"It seemed like straightaway, something wasn't right with her," said Stosur, adding that while she never wants to take advantage of an opponent's injury, she was "not going to complain" about advancing with less than a half-hour of time on court.