Nozomi Okuhara won a titanic all-Japanese battle with top seed Akane Yamaguchi to reach the women's final at the Badminton World Federation (BWF) Korea Open.
Okuhara, the 2017 world champion who is seeded third, came from behind to triumph at the SK Handball Stadium in Seoul.
Yamaguchi, a bronze medallist at this year's World Championships, won the first game but eventually went down 16-21, 21-17, 21-14.
Okuhara will now play American sixth seed Zhang Beiwen in tomorrow's final.
Zhang, who was born in China, knocked out South Korean fourth-seed Sung Ji-hyun 21-18, 21-19.
In the men's event, another same country duel saw eighth seed Tommy Sugiarto beat unseeded Indonesian team-mate and Asian Games champion Jonatan Christie 21-13, 22-20.
He will play Chinese Taipei's fourth seed Chou Tien-chen in tomorrow's final after he fought back to oust Japan's Kenta Nishimoto, 19-21, 21-18, 21-14.
The event is a Super 500 tournament on the BWF's World Tour.