Katie Boulter has reclaimed the British number one ranking after fighting back to beat Antonia Ruzic in three sets in the quarter-finals of the Japan Open.

The 30-year-old was dethroned on Monday following Sonay Kartal's run to the final in Wuhan but knew she could overturn the 55-point deficit by reaching the last four in Osaka.

Eighth seed Boulter trailed world number 91 Ruzic by a set and a break but recovered to win 3-6 6-3 6-3 in two hours to reach her first semi-final since Queen's in June.

She will face Czech Katerina Siniakova in the last four and whatever the result will climb above Kartal and back into the world's top 50 when the WTA rankings are updated on Monday.

"[Ruzic] is a really good player, full credit to her," said Boulter. "I tried to hang tough and find a way. I was a bit lucky in the middle of the second [set] but I feel I did really well to stay there."

On facing Siniakova for a spot in the final, she added: "She's one hell of a player, extremely dangerous. It's going to be who gets the first strike in.

"I've got nothing to lose. She's been building extremely well this week, so I'm going to have to come prepared."

Boulter struggled on serve in the opening two sets, winning just 60% points behind her first serve, hitting four double faults, and facing seven break points, but grew into the match, finding success when stepping inside the baseline to put pressure on the 23-year-old Croat.

Broken in her opening service game, Boulter was gifted a route back into the first set at 4-2 when Ruzic double-faulted on break point. However, Ruzic immediately hit back, winning the next four games.

Boulter wrested back control in an increasingly scrappy second set, saving two break points in the third game to avoid going a double-break down before coming up with a crucial hold in the seventh after the pair had exchanged three successive breaks.

That hold proved the second of eight straight games for Boulter, who raced into a 4-0 lead in the decider. Although she failed to serve out the match at 5-2, she broke her opponent to love to wrap up the win.