Mendes (11-0) is considered the No. 1 challenger in the 145-pound ranks. Aldo (20-1) is one of the UFC's elite, a predator who has won 13 straight since his lone loss in November 2005.
Next up is the 26-year-old Mendes, who is savouring his moment in the spotlight.
He was in his living room watching the New Year's celebrations from New York when he saw a huge UFC poster of he and Aldo in the background in Times Square.
"It's just crazy to think that a little under three and a half years ago, I was still in college," Mendes told a media conference call. "This trip into MMA, it's been a very fast rise and it's just been an awesome, awesome experience for me.
"Just sitting there and realizing that is kind of surreal. I knew I would be good at the sport but to be fighting as a main event and for the title with 11 fights under my belt, it's just awesome, man."
Mendes started wrestling at five and went on to become a two-time Pac-10 champion and All-American wrestler at Cal Poly in San Luis Obispo.
He met Urijah Faber, a former WEC featherweight champion and current UFC fighter, during high school and went to some of his wrestling camps during college.
After his NCAA career was over, he wanted to continue competing so he moved to Sacramento to train with Faber's Team Alpha Male.
"I haven't taken a year off. Ever," he said.
Mendes lists some of the major pluses of his career — training with his friends every day and travelling the world.
"It's definitely something I'm soaking up. I know that I only have a short window in my life to do this kind of stuff. This is that time."
Faber, who lost a punishing five-round decision to Aldo in April 2010 in the WEC, has been helping Mendes prepare for his title shot. And the challenger oozes confidence.
"I feel like I'm prepared, my standup is going to be where it needs to be to get in there and fight with Jose. And I know my wrestling's going to be better so I'm stoked for this fight."
On Saturday, Mendes can expect a wild crowd at the HSBC Arena in Rio that won't be cheering for him.
But he insists the pressure is all on Aldo.
"He's the one fighting in front of his home crowd. He has the belt. He's the one that has to deal with all the pressure. I'm the up-and-comer, I'm the underdog, I'm the one coming into the fight that everyone's kind of overlooking.
"I feel confident that my skills, the things that I'm good at are going to be able to beat him."
Aldo, meanwhile, says he welcomes the attention.
"I'm anxious to hear the crowd screaming as I walk inside. I just can't wait to feel that energy," he said though an interpreter.
The 25-year-old Aldo is more than a 2-1 favourite but his unbeatable facade has shown a few cracks of late. Canadian Mark (The Machine) Hominick lost his title shot but rallied to pummel a tiring champion in the fifth round at UFC 129.
Aldo subsequently won a five-round decision over veteran Kenny Florian.
"I definitely have seen things that give me confidence," said Mendes. "I don't think Jose has any holes or any cracks in his game. I think if anything, he has some areas that aren't quite as strong as others but I don't definitely see any holes.
"I feel the same way about my game ... Definitely those last two (Aldo) fights are fights that I've watched a lot and have sat down and picked apart. It's something that's helped us put together a great game plan for this fight."
The key, says Mendes, is pressuring Aldo. If you don't, the champion will pick you apart with kicks — as he did Faber —and strikes.
Mendes believes his striking will be sufficient to hold off Aldo. And his wrestling is better than the champion's.
"I don't think any of the guys that have fought him have had the wrestling credentials or the wrestling ability to be able to get a hold of Jose, get him down and hold him down."
Aldo, who trained with lightweight contender Gray Maynard to improve his wrestling, predictably sees the fight taking a different path.
"Mendes has got a disadvantage fighting me on his feet," he said. "He’s not as good a boxer as the other guys I have faced and I don't think he can do well standing up in this fight.
"I will be looking for a knockout or a submission."
Aldo admitted the weight cut was tough for the Hominick fight, leading to speculation that he may eventually move up to lightweight (155 pounds).
Aldo says he has thought about it but will leave the decision when to make the move, if ever, to his coaches.
NOTES — An avid soccer fan and former semi-pro player, Aldo will be coming out in the colours of Flamengo, a pro club that sponsors him. ... Vitor (The Phenom) Belfort faces Anthony (Rumble) Johnson in the middleweight co-main event ... Canadians on the card are lightweight Sam (Hands of Stone) Stout of London, Ont., and featherweight Antonio (Pato) Carvalho of Ajax, Ont.