Robert Gsellman of the Mets walks to the dugout after...

Robert Gsellman of the Mets walks to the dugout after the eighth inning against the Nationals at Citi Field on Thursday. Credit: Jim McIsaac

LOS ANGELES — A decade ago Thursday, at the very ballpark where the Mets are playing this week, Robert Gsellman dominated in the biggest game of what might be the most important baseball season of his life.

May 30, 2009. Dodger Stadium. The Los Angeles Division II city championship. Gsellman’s Westchester High against Monroe.

It wasn’t even close. Gsellman, a sophomore, tossed a two-hitter in the Comets’ 11-1 win.

“Damn, 10 years?” said Gsellman, whose homecoming in the Mets’ series against the Dodgers serves as a quick reunion with many of his high school baseball teammates. “I’m a champion, baby.”

Considering the context of Gsellman’s life at the time — a recent family tragedy, a questionable commitment to baseball and school — that sentiment is a lot more than an easygoing reliever basking in the faded glory of his teenage jock days. That baseball experience at that precarious time looms as a massive life-shaping influence for Gsellman.

Eight weeks earlier, his mother, Trisha, died after a battle with breast cancer. Gsellman was 15. It would have been easy, he says now, for him to have “fallen in with the wrong crowd.” He wasn’t a huge fan of studying — he didn’t play baseball as a freshman because he was academically ineligible — and, if he’s being honest, he didn’t even like baseball that much.

“Going to a school that wasn’t one of the best schools, you can find those crowds easily, ending up on the streets and doing something bad,” Gsellman said. “Lucky enough, I had some friends that kept me on the right path and kept me on the baseball field.”

And so baseball became an escape — for a few hours at a time, at least.

“It was therapy,” Gsellman said. “Being out there with all my friends, all the kids I grew up with in my neighborhood on the team. It made me forget about everything. It was a good team.”

Good might be an understatement. The season climaxed with Gsellman’s gem in the finale, but he didn’t do it all alone. Among his most prominent memories from that day: a “humongous” pitcher’s mound, much larger than the ones he was used to on high school fields; suspended Dodgers outfielder Manny Ramirez worked out at Dodger Stadium that morning, delaying the high school teams’ entrance; and Westchester’s senior shortstop, Chris Jacobs, hit two homers. Gsellman says he could have had four, with one ball bouncing off the wall and another stopping at the warning track.

And then, of course, there was the dogpile.

“The celebration on the field here afterward was the best part, jumping all over each other,” Gsellman said.

Gsellman calls it his “coming-out party” as a baseball player. A Los Angeles Times story from that day mentions the future big-leaguer only in the last sentence, noting, “Sophomore pitcher Robert Gsellman allowed two hits for Westchester.” That game kick-started a whirlwind two years for him: comical dominance (including a 1.70 ERA and .608 batting average as a senior), frequent visits from scouts and college recruiters, and the start of his professional career. The Mets picked Gsellman in the 13th round of the 2011 draft.

Basketball always had been Gsellman’s preferred sport, and he was a standout on the hardwood for Westchester, too. But that sophomore season showed him his future might be in baseball. His casual hobby became his career, those couple of months — and his first time playing in a major-league stadium — helping to give him direction at a time when he desperately needed it.

“Just knowing what I wanted to do after what happened,” Gsellman said. “All right, what’s going to happen next? Let’s see what the baseball thing can do. Now I’m here.”

Yes, now he’s here, back at Dodger Stadium, exactly 10 years later.

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