If there's one voice above all else that motivates WBA featherweight champion Leo Santa Cruz to be at his best, it's the passionate tone of his father and trainer Jose, screaming instructions from his corner during fights. 

Santa Cruz (34-1-1, 19 KOs) remembers with a heavy heart what it felt like not to hear that voice, during his lone pro defeat in 2016 against Carl Frampton. Jose, reduced to a wheel chair during his battle with Stage 3 multiple myeloma cancer, missed most of training camp and handed over the corner duties that night to his oldest son Antonio. 

The elder Santa Cruz's recovery produced a memorable moment in January 2017 when, upon his return to his son's side, Santa Cruz defeated Frampton in their thriller of a rematch to score the biggest victory of his career. Santa Cruz, 29, offered no hesitation when asked about the reason he was victorious. 

"My dad was the difference that fight," Santa Cruz told CBS Sports' "In This Corner" podcast on Monday. "That was the missing key, right there."

Finally cancer free following lengthy chemotherapy and spinal surgery, Santa Cruz's 58-year-old father is still facing an arduous daily battle as his son prepares for Saturday's rematch against WBA secondary titleholder Abner Mares (Showtime, 10 p.m. ET) at the Staples Center in Los Angeles. 

"Right now his cancer is, thank God, in remission," Santa Cruz said. "There is no cancer we think but he is still in a lot of pain and is nauseous and throwing up all the time. Most of the time he's in pain but that doesn't stop him. He's still in the gym every day. He's right there observing me, telling me what to do. He has been there every day."

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Santa Cruz, who has won world titles in three divisions, can't help but gain an even extra level of daily motivation by watching his father's perseverance. In a way, though, it's as if both father and son are fighting exclusively for one another. 

"I always say [to myself] that if what my dad is feeling is really bad and worse than what I feel, why can't I do [more]," Santa Cruz said. "If he can do it, why can't I do it? When I come in the gym and do really good and what he wants me to do, it gets him happy and gets me motivated. I like to see him happy with a smile on his face and not thinking about the pain."

Santa Cruz is happy to have his father back in his corner and with his cancer in remission. USATSI

The father/son trainer dynamic has often been a volatile one throughout boxing history. But Santa Cruz believes things work so well between him and his father because of how honestly they communicate. While it's not unusual for the two to argue at the gym, Santa Cruz said his father never carries a grudge from one day to the next. 

"No dad is ever going to lie to you so he tells me like it is and I like that," Santa Cruz said. "I can get mad at him and stuff when he yells, but I know he is doing it for my own good."

Santa Cruz credits his father for pushing him into the sport at a young age and guiding him from a distance. But it took constant encouragement from his son for the elder Santa Cruz to finally agree to train him following his 12th professional fight. 

"He said he didn't want to be my trainer because he didn't know [enough] and didn't have any experience," Santa Cruz said. "I said he had experience and is always watching boxing and learning from other fighters. Everything was better with him, from fights to sparring. In fights, I started looking better with him and the promoter said, 'Why don't you use your father.'"

The father/son duo scored what was then their biggest win in 2015 by taking home an all-action majority decision against Mares. Santa Cruz calls it the fight that elevated him to the next level among the very best in the sport. 

Should their rematch provide the same fight-of-the-year caliber drama and excitement as the first time around, Santa Cruz is well aware that the rivalry could be elevated (especially if it becomes a trilogy) to the same conversation as prior beloved Mexican rivalries like Erik Morales and Marco Antonio Barrera. Unlike that heated feud, however, Santa Cruz says there is not hostility between him and Mares. 

"From my side, there is no hatred or anything," Santa Cruz said. "We both are fighting here in L.A. and are one of the best so we have to fight each other. Of course, it could be a rivalry like Barrera-Morales and if the fans want it [like that], we will give it to them."

The 32-year-old Mares (31-2-1, 15 KOs), who like Santa Cruz was born in Mexico but lives in greater Los Angeles, shared the same sentiments for both father and son in the opposite corner.

"I know he's going through a hard time and I respect him as an individual," Mares said. "As a person, a father, it's just tough what they're going through and I'm always wishing them the best. And God be with them.

"The first [fight] was intense and [the rematch] is going to be double that. That's why we keep addressing that the fight is going to turn out to be a fan-fest type of fight because I just know we both compete like that."