It was far from a straightforward task for the 28-year-old, though this was another reminder boxing is a young man's sport and Donaire (43-10, 28 KOs) will surely be gracious enough to step away having fallen short in his latest quest for greatness.

Masuda (9-1, 8 KOs) spoke of the respect he had for his adversary, 15 years his senior and much like against Seiya Tsutsumi in December, an ageing four-weight world champion was the topic of conversation in the build-up.

Masuda gave the Hall of Famer too much respect in the early going with his back to the ropes, allowing the Filipino to stick out his jab and tag him with deft but scoring one-two combination punches in centre ring.

There were moments where the younger man's athleticism would remind you of their stylistic differences, like when he connected clean with a right-left flurry of his own deep into round four, though it was a nip-and-tuck affair Donaire wouldn't stop working in.

Things got hairy for the veteran in round five though, an accidental head clash saw his face turn crimson red and embolden Masuda into exchanging at close-range, unloading punches in bunches and generally wearing on the determined visitor.

Masuda did his best work in the sixth, as both enjoyed success. A medical intervention to inspect Donaire's cut wouldn't stop the home favorite finding his range and landing with increased frequency, rocking Donaire before eating some defiant haymakers in response. He stuck his tongue out as if to say, is that all you've got?

Pawing at the cut over his right eye and noticeably slower to throw his punches in the seventh, Masuda floored him with a left hand at the end of a right-left combination in the frame's final seconds. The writing was on the wall.

Donaire looked worse for wear as the eighth began, his corner increasingly concerned and to compound matters, he was given a point deduction for 'stepping on the ring' to begin the round.

It was his last roll of the dice, with the corner rightly throwing in the towel after being unhappy seeing him static after absorbing yet more damage midway through the stanza.

Long-standing WBO flyweight champion Anthony Olascuaga (12-1, 9 KOs) raced out of the blocks with venom en route to a ninth-round stoppage of Jukiya Iimura (9-2, 2 KOs), despite dancing with danger by winging wildly at times against an opponent who couldn't match his pace nor punch placement.

He lamented his impatience post-fight, admitting a better performance would've been ideal - had he been slightly less aggressive, not telegraphing entries as much. Easier said than done with what was, in truth, another title defense. Unifications against the division's best - if they can be made - would sharpen his senses.

A year after losing the WBO world title against unified beltholder Rene Santiago, Shokichi Iwata reclaimed championship gold with an eighth-round technical decision win over Thammanoon Niyomtrong, who lost all but one round before the contest was prematurely halted after a worsening cut caused by a head clash in the fourth.

79-73, 79-73 and 78-74 read the scorecards at the time of referee Cesar Castanon Varela ending their encounter, midway through round eight as Iwata became a two-time world champion at the two-weight beltholder's expense.

He expressed a desire to stay busy with two more appearances in 2026, all being well, and will hope to have more success having rebuilt impressively following a short-lived first title reign.

Six months after their first meeting, Ryusei Matsumoto (8-0, 4 KOs) made sure there was no doubt this time around when going the 12-round distance against Yuni Takada (16-10-3, 6 KOs) in a commanding first defense of his WBA strawweight crown.

The savvy southpaw pitched a shutout (120-108, 120-108, 120-108) to leave many critics wondering whether there was much sense in an immediate rematch, despite the anticlimactic ending to their first meeting.

Post-fight, he stressed a desire to reproduce his skills on the world stage. Per a translation, the 27-year-old said:

"Compared to the last fight, I could clearly see the adjustments Takada made. He came in very determined and showed a lot of heart but wanted to show a completely dominant performance tonight. I believe I did, showed a clear and controlled victory. I think I've graduated from the Japanese level, so from here on, I want to fight the world's strongest fighters."

In the card's opener at featherweight, teenage hopeful Natsuki Kuramochi was held to a four-round split draw (37-39, 39-37, 38-38) by Hayato Aiko.