WASHINGTON (Kyodo) -- Japan's Kei Nishikori beat Canadian Denis Shapovalov in straight sets Thursday to advance to the Citi Open quarterfinals, while compatriot Naomi Osaka suffered a second-round defeat.
Nishikori, the seventh seed, earned a 7-6(1), 6-3 win over the No. 26 Shapovalov despite the Canadian's seven aces. The former world No. 4 didn't allow a single break point and capitalized on Shapovalov's six double faults.
In their only other meeting, the 19-year-old Canadian handed a first-round loss to Nishikori at the Mexican Open earlier this year.
Nishikori, currently ranked 20th, is making his fifth appearance at the hardcourt Citi Open since his debut in 2013. He defeated American John Isner in 2015 to claim the championship, but chose not to defend the title the following year.
The 28-year-old faces No. 3 Alexander Zverev of Germany in the quarterfinals on Friday. The pair are tied after two match-ups.
In the women's singles, Naomi Osaka was knocked out after falling in a second-round decider against Poland's No. 62 Magda Linette.
Despite beating her opponent on aces and saving eight of 13 break points, Osaka fell 6-2, 3-6, 6-3 to the unseeded Linette in their first career match-up and missed out on securing her fourth quarterfinal of the year.
After quickly losing the first set at Rock Creek Park Tennis Center, Osaka continued to struggle in the second as she repeatedly missed the baseline.
The 20-year-old Japanese gained momentum with a 4-3 lead, and went on to equalize after nailing her first ace of the match. But after play went back-and-forth in the third set, Linette broke Osaka's serve to go up 5-3 and claim the hard-fought match.
Osaka, ranked 17th, had only lost once to a player outside the top 50 this year, falling to Slovenian Dalila Jakupovic in the second round of the Nature Valley Classic in June.