Justin Weissberg is going the have some pretty serious bragging rights when he walks into Long Beach High School for class Monday.

The 17-year-old Long Beach senior won the 10k race of Sunday’s Long Island Marathon in 38:06. It was his first 10k after just beginning to run a year ago. He usually runs 5k races, but his mental and physical strength pushed him through Sunday.

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“You definitely hit something Mile Three where you’re like, ‘You got to pick it up,’ ” Weissberg said. “Usually a two-three mile race you just go right through but this race you have to pace.”

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Weissberg became interested in running after participating in the 2k beach run as a Long Beach lifeguard. He said he didn’t expect to win Sunday, but he set third or fourth place as realistic goals for himself. Then he saw his opening.

“At the beginning I was standing back because I was scared I was going to get out too fast,” Weissberg said, “but then I saw I had a chance.”

He wants to go on to compete in national racing competitions. He’s discovered his talent in the sport despite little experience. But he believes he’s getting better every race.

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“It gives me confidence,” he said. “I came a long way since I started running a year ago.”