If you didn’t know that Jack McGlynn was a 17-year-old rookie, you wouldn’t have known watching him make his first professional start in the Union’s 2-0 win at the Chicago Fire on Saturday.

That’s how well the academy product fit in on the left side of central midfield. He wasn’t spectacular, but he didn’t have to be — just normal, really, someone who wouldn’t make you miss the players who weren’t there. In 62 minutes on the field, McGlynn won seven duels, recorded four recoveries and one tackle, completed 13 of 16 passes, and took three shots.

“I thought he stepped on the field [and] was confident,” Union manager Jim Curtin said. “I’m really proud of how he helped defensively, especially coming across on the side of the diamond on the weak side and making big tackles and little defensive plays to break up things that really were valuable.”

Curtin also specifically praised McGlynn’s “calmness on the ball,” which is something you don’t always see in teenage rookies.

“In terms of a soccer brain, soccer IQ, he is at as high a level as I’ve seen for a young kid,” Curtin said.

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But the Queens, N.Y., native still had his share of nerves. After being a late-game substitute four times to start his career, McGlynn said walking out on to the field as a starter “was surreal.”

“The hardest thing to get adjusted to is just the speed of the game, and the amount of pressing the other team does is just a different level,” he said.

McGlynn’s welcome to the pros came in the early stages of the first half, when he had two shots blocked by Chicago’s Boris Sekulić in the span of a minute, on almost identical setup plays. McGlynn’s second attempt came with a wide open net after an Alejandro Bedoya cross slid through the 6-yard box, and McGlynn’s first-time shot was too low.

“I was shocked to be that open,” McGlynn said, and there was some good-natured ribbing about it in the locker room afterward.

“He was all smiles, and getting a lot of accolades and congratulations,” Curtin said, “and it’s my job to tell him that he should have scored twice, and keep him humble.”

But Curtin knew those opportunities came because McGlynn made great runs to the back post on both occasions, taking space that Fire players didn’t bother defending until it was almost too late.

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Curtin admitted that he felt comfortable starting McGlynn because Chicago “maybe has more technical players, rather than, you know, a ton of athletic, fast-paced, hard, physical players.”

If that was an allusion to McGlynn’s listed frame of 6-foot, 161 pounds, well, fans saw that side of his game on Saturday, too. It will develop with everything else as he keeps growing. But as first impressions go, this one showed lots of promise.

“His ceiling is incredibly high,” Curtin said after the game. “We thought the time was right to get him a start, and like so many players at a young age, they step up to the bell and they impress you and surprise you more often than not. You have to give them the chance, and Jack stepped up in a big way and did his job for us.”