Japanese second seed Kei Nishikori defeated three-time champion Juan Martin del Potro of Argentina in straight sets Thursday to reach the quarterfinals at the rain-delayed Citi Open.Nishikori, winner of this tournament in 2015, prevailed 6-4, 7-5 in 1 hour, 49 minutes at the Rock Creek Park Tennis Center in Washington."I think I was able to win in two sets because I made fewer mistakes than in my first match (in the second round). Overall my serve was solid," said Nishikori."It's been pretty tough," Nishikori said, referring to finishing his match in the early hours of the morning again bec…READ FULL ARTICLE
