The 27-year-old Rio Olympic bronze medalist opens with a second-round match Tuesday at the ATP Citi Open in his first match.
The 27-year-old Rio Olympic bronze medalist opens with a second-round match Tuesday at the ATP Citi Open in his first match on the Washington hardcourts since beating John Isner in the 2015 final for his 10th career ATP crown.
"I don't want to think about it too much, but I know this is a tournament I've won before. I do have good memories on center court," Nishikori said Monday.
"I think there's an advantage for past champions. I'm happy to play in a place I've won before."
Ninth-ranked Nishikori was the 2014 US Open runnerup, becoming the first Asian man in a Grand Slam final, and reached the semi-finals last year at Flushing Meadows.
But he hasn't won a title since taking his fourth consecutive Memphis Open crown in February 2016, dropping six finals since then -- last year at Miami, Barcelona, Canada and the Swiss Indoors and this year at Brisbane and Buenos Aires.
"I'm always looking to win," he said. "I'm a little disappointed not to be winning some tournaments. If I keep playing well, I'll be winning some. The chance will come if I keep working hard."
Nishikori took some time off in Japan after making a third-round Wimbledon exit. He had matched his deepest French Open run with a quarter-final effort at Roland Garros, losing to British world number one Andy Murray. But he got back to work last week.
"It has been a very good week. Trained a lot," Nishikori said. "I'm excited to be in this tournament. The court is a little faster than two years ago. It's a little hot. I make fit my tennis in these conditions."
The wildcard second seed is among five of the world's top 11 players in the field, paced by seventh-ranked Austrian Dominic Thiem and rising German star Alexander Zverev, ranked a career-best eighth.
"The field is very strong. It's going to be tough rounds," Nishikori said. "I'll try to force my tennis each match. It's going to be a great tournament."
Nishikori praised the play of Swiss star Roger Federer, who turns 36 next week after capturing his record 19th Grand Slam singles crown at Wimbledon.
"Roger is playing great again. With his age, it's something incredible," Nishikori said. "I want to play a long time but I don't know if my body can stand up."
Nishikori says he loves the challenge of playing at a time when older stars and rising talents have raised the level needed to stay competitive.
"It's a good thing," he said.
"Competition is tough. Not only are the top four playing good, young guys are coming up. It's good for tennis and good for me. I'm excited. I enjoy the challenge."