Uriel Plata did not expect to win.

But the Mexican national's business trip turned into an unexpected victory celebration early Saturday when he finished first in the Long Island Marathon weekend 5K race in Uniondale.

Plata, who sells raw materials for cosmetics, had extended his weeklong stay in the U.S. by one day just so he could run.

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"I like running, and I saw there was a race, and I just joined," said Plata, 37, of Mexico City. Clutching his trophy after finishing at 18 minutes and 32 seconds at the Mitchel Athletic Complex track, Plata said his goal had been to beat his best time of 19 minutes and 15 seconds.

"I didn't expect this at all," said an elated Plata. "I was trying to break my time and not win the race, but I did both."

Plata said he makes the annual trip at this time, and next year he hopes to run in the half-marathon. His and other races Saturday were preludes to today's marathon, half-marathon and 10K races, which start beside Nassau Coliseum and end in Eisenhower Park.

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Hundreds of people broke sweats and strides under a deep blue, clear sky at two races Saturday morning. The day's biggest race, the 5K, garnered 670 registrants, while 120 people signed up for the earlier one-mile race.

The county plans to close many streets and roads in the area on Sunday, beginning at 5 a.m. Charles Lindbergh Boulevard will be partially closed, then completely closed from 5 to 10 a.m. Wantagh Parkway will be closed from 7:50 a.m. to 3 p.m.

Other road closures include parts of Merrick Avenue, Old Country Road, School Street, Salisbury Park Drive, Railroad Avenue, Post Avenue, Jericho Turnpike, Brush Hollow Road and Carman Avenue.

The female winner at the 5K was 12-year-old Ashley Minns of Massapequa Park, who came in at 21 minutes and 54 seconds. "I knew there was another female behind me, and that just motivated me to keep my pace," said Ashley, who runs on a track team and said the sport "gives you a mental challenge that no other sport can . . . you're just competing against yourself."

For Janna Ostroff and her son Jack, the race was an opportunity to run as parent and child. "I didn't walk once," said Jack, 7, with pride to his mother, a 35-year-old Plainview educator.

Others ran to raise money and awareness in the fights against disease. Susan Borkowski, 56, an import manager from Levittown, donned a blue and white T-shirt as part of "Team Borkowski," raising money for the American Lung Association in honor of her parents, who died of lung cancer in 2012 and 2014.

"It's helped a lot with the grief process," Borkowski said. Asked what her parents would think of the roughly 30 people running for them, she said, "I think they're smiling."