Then 23 years old, Saleh was poised to follow in the lucrative footsteps of his older brother, a financial adviser, and his father, a business owner.

He was set.

And he was sobbing uncontrollably.

In February 2002, less than five months into his job analyzing multimillion-dollar loans, Robert called his brother, David, and told him he wanted to ditch financial security to pursue a dream. At least, that’s what the hulking former college tight end said when he could finally form the words.

“I was trying to get him to get a grip and talk to me,” David said. “I couldn’t understand a word he was saying. Have you ever cried so hard where you can’t even speak or breathe?”

Said Robert: “It was the kind of crying when you get the hiccups.”

Fifteen years after that call, Robert, 38, was making calls last week as the NFL’s third-youngest defensive coordinator in the 49ers’ season opener.

For the rookie, who is believed to be the league’s first Arab American coordinator, it was a strong debut: The 49ers allowed just 287 yards — their fifth-fewest in their past 38 games — in a 23-3 loss to the Carolina Panthers.

Now, he returns Sunday to Seattle, where he won a Super Bowl in 2014 while working under Seahawks head coach Pete Carroll, his most influential mentor.

For David, 41, who was at Levi’s Stadium for the season opener, the game was a reminder of the sometimes penniless path his brother traveled, and the courage it required to begin the journey. Instead of earning a six-figure salary, Robert didn’t pocket more than $800 a month until his fifth year in coaching. He spent his first two seasons living for free in the home of family friends.

He didn’t start with much, but he also began without regrets.

How many people bemoan late in life the decision to work at a job instead of pursuing a passion?

“God bless him,” David said. “There’s something to be said about someone who knows at that age that he didn’t want to be doing that. He had to travel the unknown, work pretty much for free and slave at it.”

Football was a passion for the Saleh family and their hometown of Dearborn, Mich.

Their father, Sam, was a linebacker at Eastern Michigan who spent a training camp with the Chicago Bears. Their late uncle, Ossum, was a guard at Michigan State. Robert and David also played at Fordson High, and David, who has remained in finance, is an assistant coach at Dearborn Heights Crestwood High.

When he was 5, Robert began filling his falls with football as a water boy for David’s pee-wee team. But Robert figured his 17-year relationship with the sport was finished after he was a four-year starter in college at Division II Northern Michigan.

And that’s what was expected in his community. In Dearborn, which has the highest concentration of Arab Americans in the United States, stability and proximity are prized. Robert, the son of Lebanese parents, was working less than 30 miles away from home at Comerica.

We come from a very close-knit community,” said Brian Mosallam, a Dearborn native and close friend of the Salehs who helped Robert get into coaching. “It’s a very insular community where we are always around family. So what Robert did was very different. Our kids don’t go away and live in eight cities in six years.”

Robert missed football. And he might have lived with his emptiness, if not for his father’s experience. Sam still regrets declining an offer to be graduate-assistant coach at Eastern Michigan because, as Robert says, he chose to “chase money.” Robert decided to chase the sport he felt rudderless without.

“I’d be in my cubicle and think, ‘I’m not supposed to be here,’” he said. “And I finally reached a breaking point. I knew if I went into coaching, I’d lose my girlfriend, I’d have to leave home and I wouldn’t have any money. I just reached a point where I didn’t care. I wasn’t going to live with the regret.”

The problem: How to get a coaching job.

Robert and David enlisted the help of their coach at Fordson, Jeff Stergalas, and a group of former Michigan State football players that included their uncle and Mosallam. The ex-players made calls to their alma mater on Robert’s behalf, while wondering: What was the kid thinking?

“He could have done very well (financially) and I just thought he was wasting his time, quite frankly,” said Mosallam, 43, a financial adviser who is on Michigan State’s board of trustees. “I just thought it was a crazy decision.”

Robert Saleh knew many thought he was foolish. Before he landed a job as a graduate assistant at Michigan State, he was discouraged from taking the job during his interviews. Mike Vollmer, who played at Fordson and worked in MSU’s football personnel department, was briefed on Saleh by their high school coach.

“He told me, ‘Stergalas told me you’d be overly prepared,’” Saleh said, laughing. “‘You don’t want to do this. You can make so much money in banking.’”

Instead, Saleh made $650 a month during his two seasons in East Lansing and lived with his uncle’s former MSU teammate, John Shinsky, 65, and his wife, Cindy.

Saleh repeatedly says it took a “village” for him to beat long odds. The Shinskys took him in (“You talk about a godsend,” he says), his parents gave him their blessing and financial support and his first door opened because of a flood of calls on his behalf.

At some point, though, he had to prove he could coach. And he slowly rose through the ranks with a blend of creativity and ability.

In 2004, he drove to Central Michigan and showed up unannounced at head coach Brian Kelly’s office to ask for a job. He hoped Kelly would remember recruiting him seven years earlier. Kelly did, but he had bad news: He could only offer him a defensive graduate assistant position that paid $700 a month.

Saleh’s reaction: A raise?

“I said, ‘OK, that’s great. I’ll take it!’” Saleh said, laughing.

His decision quickly paid off. A year later, Saleh landed in the NFL based on the recommendation of Texans defensive backs coach Tony Oden, a former assistant at Central Michigan.

Saleh’s position: defensive intern. His salary: $5.25 an hour.

It was the start of a six-year stint in Houston during which he was promoted to quality control coach (2006-08) and assistant linebackers coach (2009-10). He went to Seattle as a defensive quality control coach (2011-13) before serving as Jacksonville’s linebackers coach from 2014-16.

During his formative years in Houston, Saleh impressed defensive coordinator Richard Smith, whose strong recommendation landed him in Seattle, and then-Texans offensive coordinator Kyle Shanahan. The 49ers’ head coach hired Saleh in February after Saleh presented him with a bulging binder that painstakingly detailed his plan for his first nine months on the job.

“I had this coordinator book,” Saleh said. “And Kyle grabbed it and was like ‘Geez.’”

Saleh also made an impression years ago on 49ers linebackers coach Johnny Holland, a former NFL player who spent five seasons with Saleh in Houston. Holland isn’t surprised the former intern is now his boss.

“Back then, I knew he was special — such a smart and detailed guy,” Holland said. “Robert will be a great defensive coordinator in this league. And there’s no doubt he’ll be a head coach in this league.”

About his smarts: Despite no formal training, Saleh has a near-expert chess rating, and he also taught himself Vizio, the computer program NFL teams had starting using for their playbooks when he entered the league.

As a low-level assistant, he stood out because of his ability to produce mountains of work in a relatively short time. And Saleh’s tech savviness gave Shinsky, who initially questioned Saleh’s career choice, the first inkling that Michigan State’s new graduate assistant coach might have a future.

“Robert would come home every night from work and get on his computer to get plays set up,” Shinsky said. “He was so good with technology and that really enhanced his opportunity because he presented everything in an organized and detailed way.”

Saleh is a long way from living in the Shinskys’ upstairs bedroom. And he’s even further removed from the day he called his brother crying hysterically.

“It just came down to: I could make money,” Saleh said, “or coach football.”

Fifteen years later, it was noted that he’s currently doing both.

“Knock on wood,” he said. “It’s been good so far.”

Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch