Brook stepped onto the scales and tipped them at 146.7, inside the welterweight limit.
Spence, entering with a smile on his face as the Sheffield crowd booed him, weighed 146.5lbs.
Both men looked in phenomenal condition and surprisingly healthy, given that they are large welterweights.
The defending champion faced a big ask to make the welterweight limit, having jumped to middleweight last September to fight Gennady Golovkin.
Brook, who in the past has admitted he struggles to boil himself down to 147lbs, underwent a strict regime in camp with nutritionist Greg Marriott implementing an effective diet plan. That certainly seemed to have paid off as he was comfortably inside the limit on the scales and stoked the gathered crowd with a final battle cry.
“I’m enjoying myself now, refueling up, get the food in. The fun part starts, the fight. I’m ready to rock. I busted my balls, I went up and fought Golovkin and now I’m fighting the number one challenger. I want to fight the best, this will be one of the fights of the year,” he said.
“I’m not going to take a backward step, there’ll be fireworks. The sun’s out, the guns are out, we’re ready. I beat Spence, I’m the number one [at welterweight].”
— Matchroom Boxing (@MatchroomBoxing) May 26, 2017
Spence – fighting outside of North America as a pro for the first time – was equally confident.
“He looks ready. This is something I’ve waited for my whole life. I feel great, I feel strong. You’ll see the game plan tomorrow, just expect and action-packed fight. I cannot wait for tomorrow night. Timing is everything and this is my time. We are going for the knockout,” he said.
Though they’ve both successfully weighed in, they can’t pack on too much excess weight over night as they will have to take part in the IBF’s check weigh-in tomorrow morning. Neither man can weigh in tomorrow more than 10lbs above what they weighed in today.
Chief support on the bill sees George Groves take his fourth attempt at a world title when he fights Fedor Chudinov for the vacant WBA super-middleweight title. Groves, noticeably chiseled, hit the scales at 167.6lbs while Chudinov, not a particularly big super-middleweight, weighed 167.2lbs.
When probed after the weigh-in whether this is “now or never” for him, he declined to answer and cut a picture of concentration.
“I’m ready. I’ve done the weight well this time, I feel good. I will be at my best and I will beat him. We’re ready to go,” he told Sky Sports.