Katie Boulter won her first WTA 500 title by fighting back from a set down to defeat Marta Kostyuk in the San Diego Open final.

The 27-year-old Briton won 5-7 6-2 6-2 in the biggest triumph of her career so far.

After a close first set, Boulter dominated Ukrainian Kostyuk to secure a victory that lifts her to a career-high ranking of 27th in the world.

"I don't know what just happened," Boulter said after the match.

"This week has been very, very special for so many different reasons. This one is pretty amazing, I've worked very hard for it, I played some incredible tennis all week.

"Today was a complete battle, with myself as well, because I was a little bit nervous. But I managed to get over the line, and that I'm very proud of."

Boulter converted seven of her 11 break points and also saved seven of the 11 that she faced.

She recovered from 5-2 down in the first set to get back to 5-5, saving five set points in the process, but Kostyuk took the opener when the Briton double-faulted.

Boulter found her form and dominated from that point, breaking Kostyuk three times in the second set to force a decider. In the final set, she broke serve twice more and served out the match by hitting her first two aces of the match and a forehand winner on championship point.

Boulter was greeted by her boyfriend, Australian player Alex de Minaur, who flew from Acapulco early in the morning after retaining his title at the Mexican Open on Saturday.

"I want to say a small special thank you to my boyfriend," Boulter added.

"He finished last night at midnight and I really want to embarrass him. He got on a 4.15 taxi this morning and six o'clock flight to be here today, so I do appreciate it."

Boulter's only other WTA Tour was won at last year's Nottingham Open, a WTA 250 event.