Igarashi entered the fight rightfully recognized as the true flyweight champion. However, the working theory is that the Japanese southpaw was the weak link among all current lineal claimants, a similar status to that of preceding champ Sonny Boy Jaro.
With that in mind, Monday's title affair was viewed as one widely up for grabs, despite Yaegashi - at age 30 - moving up two weight classes after a string of brutal wars in recent years. The theory proved correct, as the challenger struck early and often, battering a seemingly sluggish champion and repeatedly sending him to the canvas.
Igarashi was already way too deep in the hole by the time he attempted to turn things around late in the fight. That didn't make the moment any less dramatic. Both fighters were battered and bloodied, their faces resembling the two-way brutality dished out.
Yaegashi had swelling over both eyes, but merely served as badges of honor for his amazing effort. The wide scores were well deserved in favor of the all-action star, who now begins his second title reign.
The win advances Yaegashi's record to 17-3 (9KO) as he continues to land in the middle of time capsule events. Igarashi was valiant in defeat as he falls to 17-2-1 (10KO) in his second attempted title defense.
Two boxing seasons ago saw Yaegashi claim a strawweight belt with a 10th round knockout of Pornsawan Porpramook. The bout became a You Tube classic and eventually earned distinction as 2011 Fight of the Year.
His reign was short-lived, though certainly not short on drama or historic moments. Yaegashi went tooth and nail with countryman Kazuto Ioka, dropping a split decision in a fantastic war. The bout marked the first time two Japanese fighters ever faced each other in a unification bout.
Neither fighter remained a strawweight after the fight. Already faced with the threat of being stripped of a title, Ioka ditched one title and then kept the other on ice for his stablemate Ryo Miyazaki, who defeated Porpramook for that very belt last New Year's Eve. The same show saw Ioka move up to claim a paper title in the junior flyweight division.
Less than a week after that saw the ring return of Yaegashi, who struggled at times in a flyweight tune-up bout. It turned out that the 30-year old merely needed time to grow into a new weight class.