Nick Kyrgios, of Australia, poses with the trophy after he defeated Yoshihito Nishioka, of Japan, during a final at the Citi Open tennis tournament, Aug 7, 2022, in Washington. (NICK WASS / AP)

Nick Kyrgios ended a three-year title drought with a dominant victory over Yoshito Nishioka at the Citi Open on Sunday and the Australian said he was stunned at his "incredible transformation" over the last year.

Kyrgios launched a dozen aces on the way to a 6-4 6-3 win over hisJapanese opponent to claim his first singles title since winning the same hardcourt tournament in 2019 in Washington, DC.

Kyrgios, who finished runner-up at Wimbledon last month, seemed overcome with emotion as he slumped to his back on the court after sealing the win for his seventh career singles title.

To see where I was at last year to now, it's just an incredible transformation. There are so many people who have helped me get there, but myself, I've shown some serious strength to just continue and persevere and get through all those times and be able to still perform and win tournaments like this one.

Nick Kyrgios, tennis player

"To see where I was at last year to now, it's just an incredible transformation," he said, adding that he had been in "some really dark places".

"There are so many people who have helped me get there, but myself, I've shown some serious strength to just continue and persevere and get through all those times and be able to still perform and win tournaments like this one."

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Kyrgios, well known for his on-court antics and outbursts, opened up on his mental health struggles earlier this year, saying he had suicidal thoughts and the time around the 2019 Australian Open was one of his "darkest periods". 

He said last year he was unsure how long he would continue playing professional tennis but he has shown a new level of consistency this season.

Kyrgios did not drop serve in Washington and has won 11 of his past 12 matches, losing only to Novak Djokovic in the Wimbledon final.

Nick Kyrgios, of Australia, returns a shot against Yoshihito Nishioka, of Japan, during a final at the Citi Open tennis tournament, Aug 7, 2022, in Washington. (NICK WASS / AP)

He also picked up a third doubles title of the year, returning to the court with Jack Sock later on Sunday to defeat Ivan Dodig and Austin Krajicek 7-5 6-4. Kyrgios won the Australian Open and Atlanta doubles titles with countryman Thanasi Kokkinakis.

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"Before Australian Open, I decided that I really wanted to put in a good training block, and then things just started falling into place," said Kyrgios, whose ranking rose to 37th.

"I had a great Australian Open. I felt like the tournaments after Australian Open I was kind of reinventing myself a little bit on the court.

"I feel like my motivation is a lot higher than it used to be ... I don't know. I just feel like there is a small window I should capitalize on it."