The 18-year-old Nakashima, from San Diego, is playing in his first tour-level tournament. With two wins this week, he's the youngest Delray Beach quarterfinalist since Kei Nishikori won the title in 2008.
"I was just hoping to play a good match in the first round," Nakashima said. "After winning these two matches, I've gained a lot of confidence in my game, and hopefully I continue playing well. I always knew I had the game to compete with these high-level pros, and I just needed the opportunity."