There wasn't much to choose from early in the main event. Ioka, eyeing a title in his third weight class, was the more active boxer, although not landing anything of consequence. Ruenroeng landed the more telling blows when he chose to let his hands go, but the weight-drained Thai boxer was flat-footed and content to play the role of counter puncher.
Round three produced the first decisive frame in either direction came. Ruenroeng squared up his shoulders and connected with a right uppercut, splitting the guard of Ioka while stopping him in his tracks. The lack of a follow-up had Ruenroeng playing with fire fighting on the road, even in the presence of neutral officials.
Ioka picked up the pace, particularly with a steady body attack in the middle rounds. Ruenroeng was still scoring with the heavier blows, with another big uppercut connecting in round four and scoring in combination in round five. Ioka showed no fear, persistently marching forward as he refused to be buillied by the thicker-framed Ruenroeng.
The strategy didn't have much of an effect on the judges. Ioka boxed well in the middle rounds, but Ruenroeng was suddenly more active energetic, perhaps fully replenished after having earlier struggled to come within the maximum allowable weight gain mandated by the International Boxing Federation (IBF), whose title was at stake. Both fighters made weight during Tuesday's weigh-in, but the IBF only allows a 10% cap of weight regained by the morning of the fight.
Ruenroeng came dangerously close to having to forfeit his title, but somehow came within the limit to still enter the fight as defending champion.
The news wasn't good for Ioka, who was unable to keep the Thai boxer at bay during the second half of the contest. Ruenroeng's aggression cost him a point in round ten, as he was penalized for holding and hitting on the break.
There was concern that such a deduction would prove costly on the road. However, Ruenroeng's more pronounced blows were rewarded over Ioka's body attack and boxing, as indicated by the final scorecards.
Judge Pawel Kardyni somehow saw Ruenroeng pitching a shutout in the fight, save for the point deduction. The Polish official also turned in the widest tally in the evening's co-feature, when Katsunari Takayama rode two knockdowns to an otherwise close-but-clear win over Shin Ono in their strawweight title fight.
As was the case in the co-feature - with matching scores of 115-111 also in favor of Takayama - the two other judges were closer to reality in their cards. The deduction gave Ioka the win on one card, but the 115-112 score turned in by Eddie Hernandez denied the 25-year old Japanese boxing star his bid to become a champion in three weight classes.
Ruenroeng remains champion as he improves to 13-0 (5KO) with the win. Still a week shy of two years in the pro ranks, the 34-year old Thai boxer has emerged as one of the best flyweights in the world thanks to his rich background in combat sports well before turning pro in 2012.
Included in his past is a 2007 amateur win over Ioka, who falls to 14-1 (9KO) in suffering his first defeat as a pro. The fight in the amateurs was man versus child - Ruenroeng was 27 at the time while Ioka barely 18 years old - yet the same result played out in the pro ranks.
As a result, Ioka remains beltless for the first time since the moments before his strawweight title win over Oleydong Sithsamerchai, which came in just his 7th pro fight. The 25-year old is 8-1 overall in title fights, which accounts for 60% of his pro career. Included among the lot is his June '12 strawweight title unification win over countryman Akira Yaegashi in a 12-round raw.
Yaegashi presently serves as the World lineal flyweight king, with a rematch heavily rumored had Ioka prevailed. Such a fight can still occur, but doesn't quite carry the same luster.
Instead, it's Ruenroeng whose future looks bright. Already being rumored is a potential showdown with unbeaten two-time Olympic Gold medalist Zou Shiming, who - having just turned pro 13 months ago - is already being steered towards a world title.
As mentioned earlier, the undercard saw Osaka's own Katsunari Takayama score two late knockdowns en route to a 12-round points win over countryman Shin Ono in their strawweight title fight. A full recap can be found HERE
Both bouts aired live on TBS-Japan.