Anthony Joshua is approaching his fight with Joseph Parker as if he is the challenger despite holding two of the major world heavyweight titles.
Joshua weighed in 12lbs lighter than in his previous bout with Carlos Takam in October, when he won via technical knockout in the 10th round but was criticised for an apparent lack of stamina.
The Briton tipped the scales at 17st 4lbs 2oz while Parker came in at 16st 12lbs 7oz at Friday's weigh-in.
Joshua owns the WBA, IBO and IBF world titles and is looking to add Parker's WBO strap to his collection with victory in Cardiff on Saturday.
Both fighters are undefeated but Parker is the clear underdog for the bout. However, asked how he thought the New Zealander looked at the weigh-in, Joshua told Sky Sports: "Phenomenal, I know he's been training hard, it just shows that he's been putting the miles in, putting the rounds in and he's come in fantastic condition.
"I'm happy that I'm facing a lively challenger and I'm confident I'll get the job done.
"He's nimble, he's quick. I can control him but I think the lighter I am the more I'll be able to match him for speed.
"Even though in the eyes of the people I'm heavyweight champion of the world, in my mind I'm a challenger.
"Scrap my belts, I'm challenging for the WBO heavyweight championship of the world, that's what I'm going for, that's my mindset."
Teasing what would be a highly anticipated unification bout with WBC champion Deontay Wilder, Joshua added: "I haven't spoken about it much but, providing I do get this win, god willing fingers crossed, we're going to see history late 2018 and become undisputed heavyweight champion of the world."
The fight will be televised by Showtime in the United States and Sky Sports Box Office in the UK.