WATCH: Nishikori rallied from a set down to upset No. 7 seed Cameron Norrie and reach the Citi Open quarterfinals.

Kei Nishikori is finally playing like himself again.

The 31-year-old from Japan, fresh off reaching the singles and doubles quarterfinals of the 2020 Tokyo Olympics as a home favorite, is into the Citi Open quarters—his fourth of the season—defeating Cameron Norrie in three sets. He says it's the best he's played since undergoing right elbow surgery in 2019.

"I feel like it's been two years since I felt like this," Nishikori told press at Washington, D.C, where he next plays Lloyd Harris. ''The way I feel on the court is very nice, very comfortable, being aggressive. I'm finally start to feel the ball. So, to feel like [I can] beat top 10, it's been two years also."

That's showing in almost his entire game. "There are less unforced errors, and like, small differences when I have to reach with my slice and making everything, that I didn't have couple months ago," he said. "Forehand is feeling good now, so I can be little more aggressive than before."

But there's still another thing he's looking for following years of injury problems and layoffs. "I just need little more confidence," Nishikori said.

That's something he hopes he can get at his scheduled hardcourt warmups at Washington, Toronto, and Cincinnati going into the US Open, where he is a former finalist.

"I feel like these two weeks, it's going to be very important, I mean, these three weeks in U.S. series. I really want to do good before US Open," he said.

A former world No. 4, Nishikori is currently No.67 in the rankings.