Japan’s Yoshihito Nishioka upset seventh seed Karen Khachanov 7-6(2), 7-6(1) Thursday to reach the Citi Open quarterfinals. The world No. 96 fought back from 1-4 down in the second set at Washington’s William H.G. FitzGerald Tennis Center for his first career win against Khachanov, avenging his loss to the Russian at last summer’s Tokyo Olympics. “Today I really wanted to beat him,” Nishioka told ATPTour.com. “It was a very, very close match, but today I figured out how to beat him.” The 26-year-old Nishioka defeated American Jenson Brooksby and Australia’s Alex de Minaur on his way to the thi…