But the season did not always look so bright for Manzano, 26. He had been successful since he began racing in middle school, and heavy expectations led to inconsistency.

The turning point came in July, after one of Manzano’s worst performances. In Monaco, he placed last in the 1,500, the race in which Andrew Wheating ran the sixth-fastest time by an American.

“He was ecstatic, like a little kid,” Manzano said of Wheating. “It reminded me: I used to be like him, not really caring, just going out and having fun. That was the start of my loving the sport again.”

Had Manzano not regained his passion, track and field might have lost one of its biggest engines. Tests have shown that Manzano has a higher aerobic capacity than Lance Armstrong and the heart size of a man over 6 feet tall.

Manzano, said Ed Coyle, director of the Human Performance Laboratory at the University of Texas, can consume 82.2 milliliters of oxygen per kilogram of body weight per minute — a capacity that, Coyle estimates, only 10 runners and 10 cyclists in the world can match. His large heart (revealed in an echocardiogram) means that Manzano can pump more blood and oxygen to his muscles than most men his size.

“They said I have the engine of a Ferrari in the body of a Pinto,” Manzano said, laughing.

Manzano’s hardscrabble roots might have contributed to his unusual toughness. He was born in the central Mexican town of Mojoneras, where education ceased by fourth grade, running water did not exist and electricity was practically unheard of — even in 1989 when his parents, Jesus and Maria Lourdes, moved 4-year-old Leo and his younger sister, Laura, to Texas’ Hill Country.

His father took a job crushing boulders at a quarry; Leonel was left to make sense of school.

In the seventh grade, a friend persuaded Manzano to try cross-country, but at home, sports were viewed as a waste of time.

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But he had talent.

In the eighth grade, Manzano ran 800 meters in an astounding 1:55. As a freshman, he won the first of his nine Texas high school track and cross-country titles while training only 25 to 30 miles a week.

“My most important role with him was to make sure I had the entry fee paid and the bus gassed up,” Kyle Futrell, Manzano’s coach at Marble Falls High School, said, half-joking.

All the while, Manzano needed to help his family financially. He got his first job at 11. Later, his father would drop him off at school at 5 a.m. and Manzano would juggle practice at 6:15 a.m., his schoolwork and late shifts at an Italian restaurant until he became, in 2004, the first in his family to earn a high school diploma.

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Then he became a student at the University of Texas, which confused everyone. “My parents never had any experience with college kids, and I didn’t know what I was supposed to do because I didn’t know anyone else who had been to college,” Manzano said. One day he packed his gear and said to his mother, “O.K., I’m out of here.”

“She didn’t know I was going away for a while,” Manzano said.

Running eased his transition because, he said, “I was always included in a group.”

As a college freshman in 2005, Manzano doubled his weekly mileage and won the N.C.A.A. 1,500 final in 3:37.13, roughly the equivalent of a 3:55 mile.

“That wasn’t my X’s and O’s,” said Jason Vigilante, the coach of the Longhorns. “In Leo’s world, those don’t mean much.”

Manzano said: “When you start talking plans and strategy, then you have a lump of information in your mind that you’re trying to process when you’re trying to race. Sometimes it’s better to let go.”

As a sophomore, Manzano placed third in the 1,500 at the United States nationals, behind the Olympians Bernard Lagat and Gabe Jennings.

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In defeat, Vigilante said: “I’d try to find silver linings. ‘You lost, but you lost to Bernard Lagat’ or ‘You didn’t win, but you ran a great time.’ ”

“He’s incredibly gracious of his opportunities,” Vigilante added, but internally, “these consolations are meaningless.”

Lagat recalled: “Woo, this kid from Texas is really good. I told him, ‘Next year, you’re going to do very well.’ ”

At the 2007 nationals, Manzano outkicked Lagat, an Olympic silver and bronze medalist in the 1,500, finishing second to Alan Webb. All three are to compete Sunday.

Manzano and Lagat met again at the 2008 United States Olympic Trials in Eugene, Ore. This time, the Kenyan-born Lagat prevailed, with both men making the Olympic team along with Lopez Lomong, a native of Sudan.

Financial help from Jesus Manzano’s employer and thousands of dollars in local donations enabled Manzano’s parents to take their first airplane ride — 7,000 miles to Beijing. Jesus Manzano walked up to the Bird’s Nest stadium wearing a cowboy hat and said it felt as if “it wasn’t really us there.”

Leonel made it through the heats but was eliminated in the semifinals. It was only his third international meet.

“I gave it a shot,” he said. “I just wasn’t ready.”

As he prepares to end his best season on Fifth Avenue, and as he looks toward the 2012 London Olympics, Manzano said, “I feel I’m ready now.”