Gennady “GGG” Golovkin (35-0) and Kell Brook (36-0) both have perfect records as professional boxers, but that will change on Saturday night. A combined 71-0 in their careers, Golovkin and Brook will meet in the ring at the O2 Arena in London.

While Brook holds the IBF welterweight title, he’ll be challenging Golovkin for his middleweight belts. The Brit will fight in front of his native fans, moving up two weight classes to face the sport’s most feared fighter.

“Everybody he’s fought, I would beat and vice versa,” Brook told USA TODAY Sports in a phone interview. “This is a test. He’s fighting an unbeaten fighter. I have the pedigree and style (to beat him).”

Golovkin is the favorite, looking for his 23rd straight knockout, and his last three fights have ended in the eighth round or earlier. Brook has won seven of his last eight fights by early stoppage, and he weighed in slightly heavier than his opponent on Friday.

Gennady Golovkin Middleweight champion Gennady Golovkin is boxing's most dominant fighter. Photo: Getty

"The difference is, when I've seen Kell Brook at a [welterweight] weigh-in, I go backstage and he can't even get off his chair," Eddie Hearn, who promotes Brook, told ESPN.com. "Now I went in there, and you know he's made weight [comfortably]. You can see it in his face."

A championship bantamweight bout between titleholder Lee Haskins and and Stuart Hall is set to go on before Golovkin vs. Brook, but it won’t be broadcast on TV.

Start Time: 5:30 p.m. ET

TV Channel: HBO

Online Stream: HBO Now