Japan's undisputed super-bantamweight world champion Naoya 'Monster' Inoue and Mexican challenger Luis Nery both made weight Sunday for their title showdown at the 45 000-plus seater Tokyo Dome.
Boxing returns to the famous venue on Monday for the first time 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.
The unbeaten Inoue (26-0, 23 KOs), who will put his four world titles on the line, weighed in 100g under the limit at 55.2kg, while Nery came in with 500g to spare at 54.8kg.
Nery (35-1, 27 KOs), a former two-division world champion, was stripped of his bantamweight world title in 2018 after failing to make weight for a fight in Japan.
"I knew he would make the weight," said Inoue.
"It's a big event and Nery is probably making more for this fight than any previous fight in his career. I wasn't worried."
Inoue knocked out Marlon Tapales of the Philippines in December to become the second undisputed world champion at two different weights since the four-belt era began in 2004. American Terence Crawford was the first man to achieve the feat.
Inoue is fighting at super-bantamweight for only the third time, after beating both American Stephen Fulton and Tapales last year for a clean sweep of the titles.
"In terms of preparations, this is my third time and I think I have got to grips with it," he said.
Inoue's younger brother Takuma will defend his WBA bantamweight world title against fellow Japanese Sho Ishida on the undercard.
Australia's WBO bantamweight world champion Jason Moloney will also defend his belt against Japan's Yoshiki Takei.