BOSTON — Something unusual happened when Meb Keflezighi, far ahead of his competitors, began passing some of the elite women who had started before the men on Monday in the Boston Marathon. As he charged by, many of the women — exhausted and in pain — cheered him on.

Three years ago, Keflezighi was widely considered to be on the downward slope of his marathon career. He had lost his Nike shoe sponsorship. His best running days were probably behind him.

Keflezighi managed to find a new shoe sponsor, but the company was not exactly a powerhouse in the running world. He was picked up by Skechers, a brand primarily known for skateboard shoes.

On Monday, Keflezighi, who turns 39 in two weeks, introduced the running world to Skechers as he and his red and silver sneakers stepped across the finish line of the Boston Marathon a good 11 seconds ahead of anyone else.

Keflezighi was the first American man to win the race in more than 30 years.

The story of Meb Keflezighi, the oldest Boston Marathon winner since at least 1930, would have been resonant any year.

But his surprising victory was especially powerful this year, the first Boston Marathon since the 2013 bombing that killed three people, wounded hundreds and ravaged an exultant city tradition more than a century old.

“This is probably the most meaningful victory for an American because of what happened last year,” he said. “I’m almost 39. I just ran a personal best. I just won the Boston Marathon. I feel blessed.”

After 2 hours 8 minutes 37 seconds of hard running, Keflezighi stepped across the finish line at Boylston Street with his arms spread nearly as wide as the finish tape, nearly as wide as his smile. The record-setting crowd got a clear view of his bib which read, simply, “Meb.”

To the deafening cheers of the throngs that gathered to watch the race, Keflezighi changed Boylston Street from a place remembered for the carnage that happened there into a place for celebration and delight.

Keflezighi gave fist bumps to the enormous crowds in the finish area, not far from where the blasts occurred. He was embraced by the 1983 men’s champion, Greg Meyer, the previous American man to win the race. He shook hands with Jeff Bauman, who lost his legs last year when he attended the race to cheer on his girlfriend, Erin Hurley. On Monday, Bauman and Hurley returned to the finish line — the two are now engaged and expecting their first child.

The race, the world’s oldest annually run marathon, felt like a catharsis for this city. A crowd of one million people, twice the usual number, showed up to cheer the runners, which featured 36,000 athletes, 9,000 more than usual.

Twice as many law enforcement officials patrolled the racecourse as well, a sobering reminder of just one way that the blasts had reshaped the race.

The list of winners of all major marathons in recent decades is dominated by Kenyans and Ethiopians. (Wilson Chebet and Frankline Chepkwony, both of Kenya, finished second and third this year.) Runners from those countries had won 24 of the 30 Boston Marathons since 1983.

Nothing about Keflezighi’s story fits history or convention.

One of 10 children, Keflezighi (pronounced kah-FLEZ-ghee) fled to Italy from Eritrea with his mother and his siblings while his father worked cleaning jobs to support the family while arranging for them to immigrate to San Diego. In the seventh grade, he ran a 5:10 mile. (On Monday, he sustained a pace of 4:54 over the 26.2 miles.) He was a high school champion who went on to thrive at U.C.L.A. and then win a silver medal at the 2004 Athens Olympics.

At age 34, Keflezighi won the 2009 New York City Marathon, becoming the first American winner in that race since 1982.

On Monday, a moment of silence was held at 8:45 a.m. to honor last year’s victims.

Keflezighi and Josphat Boit pulled away from the pack midway through the race. Once the runners hit the hills of Newton, about 10 miles from the finish, Keflezighi made his pivotal move. “He was so far away,” said Chebet, the runner-up. “I couldn’t see Meb. I only saw straight road.”

Keflezighi said he fought off a stomach ailment around the 20th mile and then “prayed a lot” to make it to the finish line ahead of the fast-closing Kenyans.

Chebet finished in 2:08:48. The defending men’s champion, Lelisa Desisa, who is 15 years younger than Keflezighi, dropped out near the 22-mile mark, race officials said.

Rita Jeptoo of Kenya defended her women’s title, pulling away in the final three miles to easily win Boston for the third time. Jeptoo, 33, set a course record, 2:18:57.

Each winner receives $150,000, but Keflezighi said that the victory was worth far more than the amount written on the congratulatory check.

“My career is fulfilled,” he said. “Since 2008, it’s been frosting on the cake. It’s just getting better and better.”

The New York Times