Kei Nishikori is working hard to end his long wait for a 12th career title and is optimistic a return to Washington will provide the spark needed.

Nishikori has managed to reach two ATP finals in 2017 – at the Brisbane International and the Argentina Open – but he lost to Grigor Dimitrov and Alexandr Dolgopolov respectively.

The 27-year-old has not tasted success for over 16 months, with his most recent tournament victory coming at the 2016 Memphis Open after he beat America’s Taylor Fritz 6-4 6-4 in the final.

Japan’s number one did reach the French Open quarter-finals this year but he also suffered disappointing early exits at the Australian Open and Wimbledon – departing at the fourth and third round respectively.

The world number nine will be hoping to put a stop to his long title drought at the Washington Open this week, a tournament he won back in 2015 when beating home favourite John Isner.

Nishikori, who is 9.50 to win the US event, is expecting a difficult challenge due to the star-studded field, but is optimistic of adding another title to his collection.

“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. “The field is very strong. It’s going to be tough rounds. I’ll try to force my tennis each match. It’s going to be a great tournament.”

Canada’s Milos Raonic is the 6.50 favourite to lift the trophy while Juan Martin del Potro, who is enjoying a resurgence in his career after an injury-free time, is a 9.50 chance.