In December, Sadam Ali, who began boxing at age 8, fulfilled a lifelong dream by winning a junior middleweight world title. But he is by no means content.

In fact, Ali still carries a bit of a chip on his shoulder despite scoring the biggest victory of his career. He won a well-earned unanimous decision to take the belt from heavy favorite and future Hall of Famer Miguel Cotto, sending the four-division world champion and Puerto Rican legend into retirement with a loss in what was promoted as his farewell fight.

Ali ruined that retirement party and now he is set for his first defense against hard-hitting late replacement Jaime Munguia on Saturday (HBO, 10 p.m. ET/PT) at the Turning Stone Resort Casino in Verona, New York.

"I enjoyed my time off and now I'm really happy to get back," Ali told ESPN on Wednesday. "Beating Cotto was a big confidence boost. I feel like I get a little more respect now. Not all the respect yet, because some people still like to discredit my win a little bit, but it was a big accomplishment for me.

"A lot of people like to make little excuses or try to downplay my win when really they counted me out of that fight and thought there was no way I could have done it. But I knew that I could. They say he was really old or he hurt his [arm] in the seventh round and they try to downplay it."

Cotto did tear the biceps in his left arm during the seventh round and Ali took over the fight down the stretch to win a decision and the title, 116-112, 115-113 and 115-113. Ali won the final four rounds on all three scorecards to seal the deal in his first fight at 154 pounds after moving up from welterweight, where he had failed in a bid for a vacant world title against Jessie Vargas in March 2016.

"...I know Munguia is a strong and he's got power. He's tall and he's coming up in boxing. He's hungry, so I see him as trying to take my spot. But I'm not going to let that happen. I'm going to fight smart. My plan is to take him to school and I'm going to win. Simple." Sadam Ali

Cotto's injury was a factor in the degradation of his performance in the second half of the fight, but injuries happen during fights and Ali fought the fight of his life. Yet he feels like he has more to show the public.

"That was my first fight at 154 and I definitely have a lot more to prove," he said.

Eric Gomez, the president of Golden Boy Promotions, which promotes Ali, said he loves his attitude and is not at all concerned Ali might still be celebrating his big victory over Cotto and not totally focused on Saturday's fight.

"I like the fact that he thinks that way and that he's still hungry and still wants to prove he belongs," Gomez said. "Just like in any sport, once an athlete or a fighter feels content they lose that edge or hunger and it could be a problem. So I like that he feels he has more to prove and that he wants to prove the doubters wrong."

Gomez said Ali is as hungry as ever. He said that Ali and his father/manager David Ali have designs on an eventual fight with middleweight star Canelo Alvarez.

"Sadam wants the big fights. He and his dad said, 'If we get past this guy get us Canelo, we want to fight Canelo.' They have the right attitude," Gomez said. "They should be an example to the champions out there. You can't be content or satisfied with your accomplishments. You keep striving, you keep hungry and you want more. Only the strong survive. The guys who are hungry edge out their opponents. He says he's got more to prove and that's one thing I love."

Sadam Ali, right, won a junior middleweight title by defeating Miguel Cotto last December. Al Bello/Getty Images

Ali (26-1, 14 KOs), 29, of Brooklyn, New York, was originally supposed to face mandatory challenger and former world titleholder Liam Smith (26-1-1, 14 KOs), 29, of England, but he withdrew two weeks ago because of a skin condition that left him unable to train.

Mexico's Munguia (28-0, 24 KOs), 21, who had been training for a fight on May 12, had been a leading candidate to replace Alvarez on May 5 against unified middleweight champion Gennady Golovkin, but the Nevada State Athletic Commission let it be known it would not approve the bout because of the weight and experience difference. So when Munguia was offered the title fight with Ali, he took it immediately.

"I got a guy who is more dangerous than Smith," Gomez said. "He's younger, he's stronger and he's hungry. I think this is a dangerous fight because of the unknown. With Liam Smith we knew what we were going to get."

Ali, anxious to get a fight in before the start of Ramadan on Tuesday, didn't want to postpone his HBO date so he accepted the opponent change without an issue.

"After an opponent drops out some champions would have said, 'Hey, let's postpone the fight. Let's get another date,'" Gomez said. "But [Ali] came to me and said, 'Get me somebody else, I don't care who it is. Get me anybody.' That's a great attitude. They weren't picky. Sometimes a champion can be picky and choosey and it becomes difficult to come up with a replacement. In this case I was able to get it done in two days because they said, 'Get us anybody as long as the WBO and HBO approves it.'"

Ali said changing opponents is not a huge concern for him. He equated the situation to what it was like in his amateur days -- he was a 2008 U.S. Olympian -- when he would go to a tournament and fight an opponent in the draw he knew nothing about.

"It's a big change because through training camp you're focused on one guy and mostly one style, but I've been boxing since I was 8 years old and I had a lot of amateur fights, and you have no idea how the guy fights most of the time or what kind of style he's bringing to you," Ali said. "Mentally, I'm prepared if I have to do that. This is boxing, things like this happen."

Ali did point to one factor that at least concerns him a little bit about Munguia, who has never faced a top opponent. Ali is 5-foot-9 and similar in height to Smith, but Munguia is closer to 6-foot-1.

"That's the only big difference for me," Ali said. "That's a big change, the size. But I know Munguia is strong and he's got power. He's tall and he's coming up in boxing. He's hungry, so I see him as trying to take my spot. But I'm not going to let that happen. I'm going to fight smart. My plan is to take him to school and I'm going to win. Simple."