Masamichi Yabuki has done it once again.

Having passed his divisional test against Angel Ayala with a 12th-round stoppage in March, the 33-year-old was relieved as he commiserated Felix Alvarado after repeating the trick in his first IBF flyweight world title defence back at the Aichi Sky Expo Arena on Saturday.

Since losing the WBC junior flyweight strap to Kenshiro Teraji in a third-round stoppage during their March 2022 rematch, The Ring's No. 5-rated flyweight endured a sluggish start against a determined challenger who asserted himself early.

Alvarado (42-5, 35 KOs) was busy and on the front foot in the early going, Yabuki boxed well enough off the back foot but wasn't doing enough to deter the pressure as he landed punches in bunches and sought to rough-house in close.

A year to the day since his 12-round majority decision win over Tobias Reyes, the Nicaraguan was keen to show he hadn't lost a step and actively took the fight to an in-form champion with wide hooks and clever body work.

They exchanged clubbing blows at close-range near the ropes in round three, while he repeatedly tagged the IBF champion in the fourth behind the same exhausting gameplan, which worked a treat.

Yabuki (19-4, 18 KOs) kept him honest with jabs and work downstairs as they entered the second-half of a gruelling tussle, curling hooks and uppercuts to the midsection as Alvarado winced in his corner before round eight.

That visual was perhaps in acknowledgement of the exhausting pace he needed to maintain - that he did - mirroring Yabuki's earlier work to the body and the champion continued working adequately off his back foot.

Not given a moment's rest, constantly backed against the ropes and needing to be clever with his punch selection, Yabuki tried restoring some order behind his jab late in the 10th.

He spun Alvarado into a corner and displayed some smart movement, though needed a moment of inspiration to really turn the tide in a fight that could've gone either way with two rounds remaining.

Right on cue then, Alvarado found himself walking into a sequence of jabs before they furiously traded in the pocket. This inadvertently saw the Nicaraguan lose his defensive shape and after connecting on a trio of hooks, he ate a short counter left that wobbled him backwards and soon enough, he was on his knees with a count administered.

The crowd were visibly delighted at this sight, perhaps aware their man needed a strong finish like this and that lit the touch paper for a frantic final frame. Alvarado abandoned his defensive discipline seeking an assertive response, undoubtedly frustrated at what had just transpired, though it led Yabuki to punish him with little over a minute left in their encounter.

Alvarado threw a left hook at Yabuki, nonchalantly eating it and walked forward intently. Swaying side-to-side trying to evade, the end was near as the champion crunched him with a left hand, then followed up with a short combination before he met the canvas once more.

The 36-year-old beat the count before motioning that he was okay to continue, but referee Katsuhiko Nakamura had other ideas in what proved another dramatic finish.