Naoya Inoue survives a first-round knockdown to knock out challenger Luis Nery in the sixth round in front of 45,000 fans.

Fans at the famous venue, which seats more than 45,000 people, were stunned on Monday when Nery floored the unbeaten “Monster” in the first round with a huge left.

But Inoue got up and knocked his Mexican opponent down in the following round and sent him to the canvas again in the fifth before finishing him off with a right hook in the sixth.

“It was a great feeling to knock him down, but how about that surprise in the first round?” the 31-year-old Inoue asked.

“As a boxer, when that happens to you, it fires you up. It gave me a lot of energy.”

It was the first boxing event to be held at the Tokyo Dome since 42-1 underdog James “Buster” Douglas knocked out unbeaten heavyweight champion Mike Tyson in February 1990 in one of the sport’s biggest upsets.

“There was a lot of pressure on me as the main event in the first boxing at Tokyo Dome in 34 years, but it gave me strength,” Inoue said.

Inoue took his record to 27-0 with 24 wins by knockout.

It was his first fight since becoming the undisputed super bantamweight world champion in December.

He is just the second man to become undisputed world champion at two different weights since the four-belt era began in 2004. American Terence Crawford was the first.

Fans at the Tokyo Dome gave the 31-year-old a rapturous welcome as he entered the cavernous venue with all four world championship belts up for grabs.

A huge upset looked like it could be on the cards when Nery sent the champion sprawling.

But it seemed to energise Inoue, and he came flying out of his corner to send Nery down in the second round.

Inoue continued to land ferocious blows, and he sent his opponent to the canvas again with a left hook in the fifth round.

The referee stopped the fight after Inoue downed Nery for a third time in the sixth round.

Nery, a former two-division world champion, was fighting in Japan for the first time since he was stripped of his bantamweight world title in 2018 after failing to make weight for a bout there.

He was subsequently banned from fighting in Japan, but the country’s Boxing Commission gave him the green light to compete against Inoue.

Nery was booed when he was introduced to the Tokyo Dome crowd.

The 29-year-old’s record fell to 35-2 with 27 KOs.

Inoue was fighting at super bantamweight for only the third time after beating American Stephen Fulton and Marlon Tapales of the Philippines last year for a clean sweep of the titles.

He moved up in weight class after becoming the first undisputed bantamweight world champion since Panama’s Enrique Pinder in 1972.

Earlier, fighting on the undercard, Japan’s Yoshiki Takei beat Australian defending champion Jason Moloney by unanimous decision to win the WBO bantamweight world title.

Takei started strongly before Moloney came back into the bout in his second title defence.

But the Japanese fighter, a former kickboxer who had won all eight of his previous boxing matches by knockout, took the title in front of a raucous crowd .