The 30-year-old climbed off the canvas, rallying after a fourth-round knockdown to inflict Erik Badillo's career-first defeat with a penultimate round stoppage during their entertaining title clash on a stacked show topped by Riku Masuda-Daigo Higa at Tokyo's Kokugikan in Japan.

He was grinning from ear-to-ear after two completed rounds, aware that he was bossing proceedings against a sluggish starting challenger.

Each of the first two frames were punctuated by impressive single shots that had the crowd stirring in anticipation of more, which eventually came as Iwata (17-2, 14 KOs) mixed in body attacks from Round 3 onwards.

Yet Badillo (19-1, 9 KOs) responded with his best frame in the fourth, finding some rhythm behind his punch sequences and flooring the defending champion with a left hand he didn't see coming.

The fifth was predictably tense as Iwata knew he couldn't afford to open up too much and lose his defensive shape. Badillo would be ready for counters, testing whether he'd truly gathered his bearings again.

Stiff uppercuts and work on the inside were paying dividends for the Mexican, though Iwata finished the stanza with a three-punch combination which foreshadowed a fast-and-furious pace over the next few rounds.

Badillo was wobbled twice in Round 6 as Iwata beckoned him forward. The champion's body punching gradually took a toll, though he felt a series of counter hooks whenever they engaged at close-range.

On unsteady legs as they traded, Badillo waded into dangerous areas aware this was perhaps his best way of clawing back an unlikely victory.

Iwata was conscious not to punch himself out after hurting the challenger again in the final minute of an exhausting eighth round, with referee Laurence Cole lurking alongside him.

Yet it often felt like when a finish was near, Badillo would reply with enough resistance. After absorbing two body shots and three right hands in quick succession, The Ring's No. 7 junior flyweight responded on the back foot and didn't stop punching in the tenth.

Weary as they entered the penultimate frame, you could sense his recovery powers were waning and Iwata wanted another stoppage.

Biting on feints more than he was earlier, less fluid with his movement and considerably less snap on his punches, Badillo was now there for the taking.

A big body shot and stinging right hand was among the punches prompting Cole to wave off the contest, the end coming officially at 2:14 of Round 11.

Japanese bantamweight contender Katsuma Akitsugi (14-1, 5 KOs) scored a fifth-round stoppage of Herlan Gomez (14-4, 10 KOs) and sank to his knees in celebration after returning to winning ways.

The 28-year-old, ranked No. 10 with the WBO, lost his perfect record via majority decision after a grueling 10-round battle with Mexican underdog Jose Calderon on April 11 but wouldn't be denied this time around.

Clubbing left hands and noticeably sharper to the punch during their close-range exchanges, the southpaw was guilty of brawling too much at times. Gomez countered him enough to keep the Los Angeles resident honest, before suffering cuts either side of his face.

One was from a head clash and after a brief pause, the sight of his own blood spilling prompted urgency to find a finish. He did precisely that, unloading an unanswered flurry and the referee waved it off moments later.