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 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."We both made a lot of mistakes but I had a more solid performance," Nishikori said. "I admit I wasn't perfect, but I managed to hold my serve and maintain my concentration."In their only other meeting, …READ FULL ARTICLE