Nick Kyrgios has a highest ranking of 13 in October 2016 and went into the Washington tournament ranked 52nd
Australian Nick Kyrgios said he had experienced "one of the greatest weeks" of his life as he won his sixth ATP title at the Washington Open.
Kyrgios, 24, overcame back spasms and a poor opening set to beat third seed Daniil Medvedev 7-6 (8-6) 7-6 (7-4).
He hit 18 aces and never faced a break point against the Russian, and will now move back into the world's top 30.
"This is probably my best memory of a final. I left it all on the court," said Kyrgios.
"I've made massive strides. This whole week has been amazing. It's a week I won't forget."
Medvedev, the world number 10, led 5-2 in the first-set tie-break, but Kyrgios saved a set point and then won it in 41 minutes.
Kyrgios sent down an ace to create two match points, and needed only one to wrap up victory - and his second title of the season after winning in Acapulco in March - in one hour 34 minutes.
He had beaten Medvedev, 23, in three sets in their only previous meeting, which came on the clay courts of Rome earlier this year.
The result also improved the Australian's impressive record against top-10 players this year to five wins and one defeat.
"In the past six months, it's crazy to think how much I've been able to turn it around," added Kyrgios. "I'm working hard to be better as a player and a person.
"I lost faith that I could still have weeks like this and be happy. I've got to thank [my family] for not losing faith.
"I just wanted to clean myself up and have a healthy attitude. I showed what I can do this week."
Asked what his best memory of the week was, Kyrgios - who was frequently seen in local pubs during Wimbledon - said: "How professional I was off the court.
"I've got a long way to go."