KANSAS CITY, Mo. — Most great athletes are motivated by something bigger than themselves.

Their drive may come from an array of different things — money, fame, disrespect, upbringing, family, survival.

The source of Isiah Pacheco’s drive is as unmistakable as it is unbreakable.

The 23-year-old Chiefs rookie running back, who got to Kansas City and the AFC Championship game Sunday against the Bengals at Arrowhead Stadium by way of rural Vineland, N.J., and Rutgers, is driven by family tragedy.

Pacheco’s youth was forever scarred by the loss of his brother and sister to murder in a span of less than two years when he was in high school in South Jersey. Those tragic events spurred Pacheco to a relentless pursuit of greatness.

Everyone knows the Chiefs for Patrick Mahomes. And why not? The NFL’s perennial MVP favorite has produced 45 touchdowns (41 passing and four rushing) and thrown for 5,250 yards this season.

As Mahomes goes, the Chiefs go.

But don’t sleep on Pacheco, a 5-foot-11, 215-pound can of whoop-ass who keeps opposing defenses honest, prevents them from defending only  Mahomes.

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Never has Pacheco been more important to the Chiefs than he will be on Sunday with Mahomes expected to be at least somewhat compromised by the high ankle sprain he sustained last week in a playoff win over Jacksonville.

Surely, some are surprised by what Pacheco has accomplished so quickly, going from a seventh-round draft pick project out of Rutgers to RB1 for the Chiefs, leading the team with 830 rushing yards, a 4.9-yard average and five touchdowns.

Those who aren’t surprised by Pacheco’s achievements are those who know him best, beginning with Greg Schiano, his former head coach at Rutgers.

“I don’t think anybody could have predicted that he’d be this successful this quickly, but I told everybody [scouts] who came to Rutgers to see him, ‘He’s the hardest practice player I’ve ever coached,’ ” Schiano told The Post. “I’m just so happy for him and his family. He’s worked for every bit of it. He’s overcome a lot. He had a rough upbringing. Lot of love, but a lot of trauma there, too.

“He saw some tragic things. But he’s overcome. He’s got people that love him and care about him, but there’s a lot of history there, too. I’m really excited for him. He deserves this. It’s pretty cool.”

Pacheco’s older brother, Travoise, was stabbed to death at age 29 on January 10, 2016 in Bridgeton, N.J.

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Then, on Sept. 20, 2017, his sister, Celeste, was found in her Millville home, dead from a gunshot wound to the head. The killer was a man with whom she shared a child.

In a 2019 interview with NJ.com, Pacheco said his sister “was like a best friend” to him and reflected on his brother’s death.

“My brother, if he was to see me here, he’d be shocked,” he said. “He encouraged me to play football as a kid and he never got the opportunity to see me play. Having an opportunity to play ball, it helps me a lot not worrying about the tragedies that happened. It makes me want to go harder.”

Pacheco’s arms are adorned with tattoos honoring his brother and sister.

“I play football for them,” he said.

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Kansas City head coach Andy Reid, who also has endured unthinkable family tragedy, with one of his sons dying of an accidental drug overdose and another in prison for severely injuring a young girl in an alcohol-related crash, is certainly happy Pacheco is playing for the Chiefs.

In Kansas City’s divisional playoff win over the Jaguars, Pacheco rushed for 95 yards on 12 carries and took a lot of burden off of Mahomes. He’s absolutely one of the keys for Kansas City to win and advance to the Super Bowl.

“I’ve been waiting on this moment my whole life,” Pacheco told reporters this week.

“He’s so physically gifted,” Mahomes said. “It’s hard for defenses to account for how physical he runs.”

Jay Butler, Schiano’s strength and conditioning coach at Rutgers, said he never has seen a player embrace the hard work behind the scenes as Pacheco did when he was with the Scarlet Knights.

“There’s no question he loves football; that’s No. 1,” Butler told The Post. “His motivation comes from his whole family situation. When I’ve talked to him, he’s said, ‘That’s why I go hard all the time. I can’t not go hard every day.’

“If there’s one guy that deserves to make it with the stuff he’s gone through and how hard he’s worked it’s him.”

If anyone ever were to wonder about Pacheco’s resilience and mental fortitude, he attended his sister’s funeral the morning of Sept. 29, 2017 and played in Vineland High’s 60-6 win over Cumberland Regional that evening, rushing for 157 yards and three touchdowns.

Three days after his sister’s death, he ran for 222 yards and a touchdown to lead the Vineland to a 42-6 win over Egg Harbor Township on Sept. 23, 2017.

“He’s ultimately very motivated to be great,” Schiano said. “The future’s bright for him. I just can’t wait to see him develop.”

In the many conversations he had with Pacheco about playing in the NFL, one of Schiano’s constant messages to him was about how “a lot of guys get there, get to training camps, but it’s about staying there, making it a career.”