A nervous wait for the scorecards followed an absorbing 12-round flyweight main event, though Ricardo Sandoval boxed brilliantly and never waned - even after being floored in round four - to stun Kenshiro Teraji on enemy territory, claiming the unified flyweight world titles.

Judges Leszek Jankowiak (115-112) and Joseph Gwilt (117-110) both scored it for Sandoval, in contrast to Pawel Kardyni's 114-113 Teraji card as the belts changed hands after this firefight - an upset just as the pound-for-pound talent dared to dream of achieving undisputed status before moving up again targeting Jesse 'Bam' Rodriguez at 115-pounds.

Their matchup topped a world championship tripleheader streamed live on DAZN from Yokohama Buntai in Yokohama, Japan.

Sandoval was quick out of the blocks, much to the surprise of many observers who were perhaps guilty pre-planning Teraji's next steps before this unified title defence had begun.

Up against a bullish contender with little to lose and everything to gain, Teraji was absorbing the cleaner work early before willingly engaging at close-range in the third, walking the American back towards the ropes as his punches were visibly the more impactful.

Sandoval wasn't worried by the home favourite's heat flashing in his face, more than happily flicking out his jab and pinging attacks where possible.

It would be too simplistic to say Teraji was overlooking his younger foe, Sandoval outworked him early and chained together combinations while making him work harder to attack.

However, the champion's punching power was enough to keep him honest. Just as soon as the 26-year-old was being praised for taking Teraji's shots flush, he was sent to the seat of his pants by a sharp one-two - the right hand connecting clean - a shot he didn't see.

After beating referee Steve St Germain's count, he recovered well enough as the stern resistance returned but that was all the impetus Teraji needed to believe he was in control.

Patiently the champion pressed forward, enthused by his work after a slow start as they entered the sixth.

A whipping right uppercut in the final seconds was the exclamation mark on an assertive Teraji round, Sandoval opening up more and countering well to head and body, though the older man had settled into a rhythm now - which his challenger gamely welcomed.

Sandoval replied with a sharp start to round seven, they traded downstairs and a big right forced Teraji into taking a backwards step as their intense pace persisted. Both landed big bombs and in the eighth, came more of the same as neither wanted to relinquish ground.

Keenly aware of the optics surrounding a strong finish, Teraji timed his entries well after eating more right hands to head and body. Sandoval skirted around the ring smartly in the ninth, keeping distance for large periods while nailing the Kyoto man with more attacks.

The champion's output was noticeably measured by this juncture and although counterpunching well, this contest conceivably was level through nine rounds.

Teraji tagged Sandoval with a big right hand early in the tenth, a morale-boosting shot given how the previous few minutes were unfolding, often second best to the punch and coming unstuck against a younger man whose confidence only increased after being floored.

"El Nino" was switching stances seamlessly and being rewarded for it, before a bruising 11th-round unfolded with both having pockets of success and letting their hands go wildly as the crowd noise swelled once more in anticipation of a grandstand finish.

Both fired haymakers in centre ring during a pulsating 12th round, Sandoval refusing to stop punching before Teraji wobbled him with relentless right hands of his own late on.

The final bell came not a minute too soon and Sandoval was soon lifted aloft onto one of his coach's shoulders in celebration. Teraji - sporting a swollen right eye - trudged back to receive medical attention in his corner, having expended energy aplenty and unsure what the three judges' scorecards would say. Ultimately, Sandoval proved good value for victory.