John Riel Casimero needed less than a round to prove on Sunday that he is the biggest threat to Naoya “Monster” Inoue’s status as pound-for-pound king.

In a devastating display of punching power, the Filipino three-division champion knocked out American Saul Sanchez at 2:41 of the first round at the Yokohama Budokan in Japan.

The Japanese referee intervened after a thunderous right to the head staggered Sanchez, sending Casimero and his cornermen celebrating like crazy.

So overjoyed was the 35-year-old Casimero that he did a pushup at ring center using just his left hand while Sanchez’s handlers attended to their shell-shocked fighter.

All in all, Casimero, who was overweight during the official weighin on the eve of the bout, scored two knockdowns.

Sanchez’s first trip to the deck took place just 20 seconds into the match while his second happened a minute earlier when a left hook by Casimero sent him flat on his back, his feet up in the air.

For a moment, it seemed that Sanchez’ left leg twitched as he was trying to get up and he barely beat the count.

Seeing that his opponent was in deep trouble, Casimero lunged at him, pinned him on the ropes where Sanchez got struck by hard blows to the head and body.

He succeeded in tying up Casimero but the pounding resumed on the other side before that right straight landed and wobbled him, enough for the third man on the ring to call a halt to the carnage.

During the post-fight interview on top the ring, Casimero didn’t waste time in taunting Inoue and assured everyone, including his promoter Masayuki Ito that if he ends up fighting for a world title again, he will train even better.

“If it’s a world title fight, I will train harder,” said Casimero, implying that since his clash with Sanchez was a non-title affair, he didn’t train like hell.

The smashing win boosted Casimero’s win-loss-draw record to 34-4-1 with 23 knockouts.

The loss — his first by knockout — dropped Sanchez’ mark to 21-4 with 12 knockouts.

The day before the fight, Casimero could not get down to the contracted weight of 122 lbs while Sanchez easily passed the test.

As a penalty, Casimero was told not to weigh more than 128 lbs five hours before the fight, a requirement that he was able to meet.

Also, he was made to wear thicker gloves.

But despite the disadvantages, Casimero, who is rated by three world governing bodies, rose to the challenge and kept his name relevant and in the mix for the Inoue sweepstakes.

However, it could not be determined if Casimero can fight again in Japan because of his perennial weight problems since the Japan Boxing Commission is strict in its enforcement of rules.