Nao Ikeyama said she will retire after losing her WBO atomweight crown by a split decision to Japanese compatriot Mika Iwakawa on Sunday.
In another women's world title fight, Tsunami Tenkai successfully defended her WBO light flyweight title with a fourth-round technical knockout of the Philippines' Gretchen Abaniel in Okinawa.
At Kyoto's KBS Hall, the 35-year-old Iwakawa outpointed the 48-year-old Ikeyama 2-1. Ikeyama, looking to extend her record as Japan's oldest world champion, was making her seventh title defense.
"I'd decided I would retire if I lost," said Ikeyama, who turns 49 in September. "I can accept this easily. I wasn't good enough."
Ikeyama pressed the attack, but Iwakawa responded by using her feet well and landing effective punches. Iwakawa improved her record to 8-5 with one draw, while the former champ fell to 10-3 with two draws.
The title fight was Iwakawa's second, and first since December 2016. Having lost to Ikeyama in 2013, Iwakawa was in tears after hearing the decision.
"I finally got it. It took a long time, and it still seems like a dream," Iwakawa said. "I had thought I was better technically."
At Okinawa Convention Center, the 33-year-old Tenkai, an Okinawa native, stopped Abaniel 1 minute, 33 seconds into the fourth round. Although Tenkai had trouble solving Abaniel's defense, she began landing telling blows and was able to land one punch after another in the fourth.
Tenkai, who won the WBA women's superflyweight title in March, improved to 16-9 in her career with 11 wins by knockout. The 32-year-old Abaniel is now 18-10.
"At first, it was quite difficult, but I was (eventually) able to land consecutive blows," Tenkai said. "I'm happy I could end it quickly."