RIYADH, Saudi Arabia (AFP) — Japan's unbeaten Naoya Inoue said he was exhausted after defeating Mexico's Alan Picasso by unanimous decision in Riyadh on Saturday for his fourth win of 2025.

The fighter nicknamed "Monster" successfully defended his undisputed world super-bantamweight titles for the sixth time in his first fight in Saudi Arabia.

But it was not enough to knock out the gritty Picasso, as Inoue settled for a unanimous decision win for the second fight in a row.

The 32-year-old has had a jam-packed schedule this year and he blamed fatigue for a performance that he described as "not good."

"To be honest, I'm tired," he said, after taking his record to 32 wins, 27 by knockout.

"It wasn't so much having four fights in a year as having to work hard to prepare for those four fights.

"You can put up with it at the time because you're only thinking about the fight, but now that it's over I can see that I really gave all I had," he added.

Inoue's win paved the way for a mouthwatering potential showdown with compatriot Junto Nakatani next year in Tokyo.

Nakatani beat Mexico's Sebastian Hernandez by unanimous decision earlier on the same card in his super-bantamweight debut.

Inoue stressed that nothing had yet been decided but said he would "love to make a fight happen that would get everyone in Japan excited."

Inoue had a height disadvantage of eight centimeters against Picasso, who also went into the fight with an unbeaten record, which included one draw among 32 wins.

Inoue's superior class began to tell from the opening bell, with the champion landing a series of hard shots in the early rounds.

Inoue wobbled Picasso with another concussive salvo at the start of the sixth round, before the Mexican finally began to come out of his shell and land a few punches of his own.

Picasso dug in to take the fight past the 12th and final round, although the judges' decision was by then a foregone conclusion.

It was the second straight fight that Inoue had been taken the distance, following his unanimous decision win over Uzbekistan's Murodjon Akhmadaliev in September.

"No disrespect to Picasso, but I wanted to show the difference between us a little more and to knock him down," Inoue said.

"I wasn't able to meet expectations or to box the way I wanted to."

Nakatani was given a tough lesson in the realities of the super-bantamweight division in his bout against Hernandez.

The 27-year-old looked comfortable in the first half of the fight but Hernandez refused to be beaten and slugged his way back into contention.

Nakatani did just enough to get the decision and take his unbeaten record to 32 wins with 24 knockouts.

He said the fight had been "an experience" and targeted a bout against Inoue for his next outing.

"I moved up to this division to win world titles, so if I get that chance then I want to take it," Nakatani said.