SAN DIEGO — Had the season gone according to plan for the Mets, Chris Flexen’s opportunity to impress might have been limited to a chance encounter with manager Terry Collins. On that day this spring, at a golf driving range in Port St. Lucie, Florida, Flexen briefly introduced himself, then smashed a couple of long drives that stuck in Collins’ mind months later.

Flexen couldn’t have known that a few weeks later, his scheduled Grapefruit League start would be scratched because of a sore right knee, which would lead to surgery that delayed the start of his season. Nor could he project that a few months later, an even bigger opportunity would arise.

When Flexen makes his big-league debut against the Padres on Thursday, he will become the first Mets starting pitcher since 2006 to make the leap from Double-A to the majors. Not since Mike Pelfrey has a Mets starting pitcher skipped Triple-A on the way to the big leagues.

“This is a dream come true,” Flexen said. “This is something you work your whole life for. It’s overwhelming, it’s exciting, it’s nerve-wracking. It’s all of the above. But mostly, I’m excited.”

The promotion underscores both Flexen’s own improvement, and the Mets’ lack of pitching depth, an area that had been expected to be a strength before injuries took their toll. The righthander will be the 12th starter to take the mound for the Mets this season. He joins a list that includes Tyler Pill, Tommy Milone and Adam Wilk.

“For me, if he doesn’t try to change anything when he gets here, makes his pitches, keeps the ball down, gets movement, he’ll get outs,” Collins said of Flexen. “But I’m anxious to see him pitch. I really wanted to see him pitch in spring training and start that game because I’ve heard great things about this guy.”

Flexen, 23, quickly got back on track after having bone chips removed from his knee. In 10 starts between Class-A St. Lucie and Double-A Binghamton, he’s 6-1 with a 1.76 ERA. In that span, he has shown command of a sinking fastball that tops out at 95 mph.

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“Most of all, I was just being really confident,” said Flexen, a 14th rounder in the 2012 draft. “Attacking hitters, sticking to a game plan, not trying to do too much, not afraid to make mistakes and not letting all the little things bother me.”

Though he hoped to make a run at reaching the big leagues later in the season, Flexen admitted he was stunned by his promotion, which came after Zack Wheeler went on the disabled list with a stress injury.

Flexen will be the first Mets player to skip Triple-A Las Vegas since 2015, when Michael Conforto went straight to the majors from Binghamton.

For Flexen, the chance has been the culmination of a long road. He had Tommy John surgery in 2014 and did not pitch his first full season as a professional until 2016. He pitched well enough for the Mets to add him to the 40-man roster, which earned him a spot in his first big-league camp.

Now, after just missing out in spring training, Flexen’s big- league debut will be witnessed by a large contingent of family and friends who will make the easy trip from his native Northern California.

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“It was a big bummer, first spring training, I was excited,” Flexen said. “Huge letdown obviously with an injury. But I bounced back. I’m here. I’m excited to reach the ultimate goal.”