Seiya Tsutsumi didn't have it all his own way and needed to recover from a stunning fourth-round sequence but held firm over the championship rounds to eek beyond Nonito Donaire, retaining his WBA bantamweight world title.

Just days after Noel Mikaelian made now-former WBC cruiserweight world champion Badou Jack feel old in their rematch, this determined 43-year-old counterpart fell narrowly short in seeking to become the sport's third-oldest ever world champion.

Questions over Donaire's foot speed and durability were immediately questioned during the main event of a U-Next title fight tripleheader in Kokugikan, Tokyo, Japan, against a sharp and twitchy Tsutsumi (13-0-3, 8 KOs) eager to point-score and establish early dominance.

As the battle of jabs intensified, Tsutsumi found himself gasping for air and in recovery mode in the corner at the end of a frantic fourth. He absorbed a counter right hand as he threw one of his own, then ate a big right uppercut and left hook which badly rocked him.

Donaire (43-9, 28 KOs) could smell blood, but didn't have enough time remaining to finish the job as referee Luis Pabon didn't initiate a count, instead letting them continue to fight.

The crowd noise swelled in the fifth as Tsutsumi tried turning things back his way, Donaire's pressure easing as time wore on, something that would later haunt him down the stretch.

That's because the defending champion fared far better in rounds six through nine as he composed himself again, doing better flicking out his jab and wearing on the interim beltholder with two and three-punch combinations.

It was a closely-contested affair as expected, Donaire agonisingly close to ending it early, though you don't get points for admirable stories in boxing and Leszek Jankowiak's wide 117-111 scorecard rather typified that sentiment.

Pinit Prayadsab's 115-113 Tsutsumi score felt fairer on the reflection of a back-and-forth duel, seeing the 29-year-old end his 2025 in the win column after a gruelling draw and injuries sustained against Daigo Higa in February.

In the card's chief support bout, Rene Santiago reeled off another upset win to unify the WBA and WBO junior flyweight world titles against previously-unbeaten Kyosuke Takami via split decision.

Scores of 115-113 and 117-111 in the Puerto Rican's favour saw him snatch Takami's perfect 10-0 record, as well as the WBA title after a back-and-forth battle where both looked to counter the other's success.

"He's a brave strong boxer, a very good fighter but I'm sure I have the style to beat him," the 34-year-old told The Ring in the build-up and that's exactly what transpired.

The Ring's No. 3-rated junior flyweight contender (15-4, 9 KOs) was tagged often in the latter stages of rounds, but didn't let those optics deter him, giving as good as he got against Takami, regularly baiting him into exchanging leather at close-range.

Takami (10-1, 8 KOs) only had himself to blame, getting overzealous during sequences where he'd hurt the visitor and unable to adjust against his tricky movement.

Winging wildly and cranking up the pressure, rather than remaining measured, played into Santiago's hands in the latter stages as he conserved his energy to close out a competitive but nonetheless deserved away result once more.

WBO flyweight champion Anthony Olascuaga made the fourth defence of his world title, and second in three months, another quick night's work to blitz Taku Kuwahara (14-3, 9 KOs) in four rounds.

The Ring's No. 6-rated 112-pound operator Olascuaga (11-1, 8 KOs) started fast with flurries, while the combination punching and pressure proved too much for the 30-year-old to handle as he pinned him in the corner with very little resistance coming back before referee Robert Hoyle waved it off.

The Los Angeles native was delighted to end the year with a fifth stoppage in his last six appearances and thanked the fans for making him feel welcome, in what's fast becoming his second home.

"I'm so excited to have performed so well against a great fighter like Taku, who has great speed, I really appreciate it, whether you were here to support me or him, it means a lot," the 26-year-old said when addressing the Kokugikan crowd post-fight.

Earlier in the evening, Kuwahara's agemate and 2024 foe Seigo Yuri Akui (22-3-1, 12 KOs) returned with a third-round knockout win over 10-1 pro Vencent Lacar in his first outing since March, where he suffered a heartbreaking stoppage loss in the final frame by Kenshiro Teraji of their WBA/WBC title unification.