Brandon Nimmo of the Mets runs to first Thursday on Opening...

Brandon Nimmo of the Mets runs to first Thursday on Opening Day at Citi Field. Credit: Jim McIsaac

Brandon Nimmo wasn’t smiling in his giant photo on the Citi Field scoreboard for the Mets’ home opener on Thursday, which was odd. It’s hard to catch Nimmo when he’s not smiling.

After the 4-0 loss to the Nationals, Nimmo also wasn’t smiling when he said, “I’ve been letting the team down.’’

The Mets are 5-2, but Nimmo hasn’t joined the party. After going 0-for-3 with a walk and a strikeout, the leadoff man is 2-for-23 (.087) and has struck out 14 times in 30 plate appearances.

He’s also under the weather, which is why he was looking forward to Friday’s off day. “Enjoy getting some sleep tonight and resting up tomorrow,” he said. “Come back at it ready to go on Saturday.”

Nimmo said he will resist the urge to spend too much time ruminating on his struggles before Saturday, but he has an idea.

“I think it’s mechanical,” he said. “And so I’m going in the video room to check it out. I think there’s a few things that I have my eye on, but until something clicks — I’ll let you guys know what that is when it happens.

“It’s all trial and error. Right now we’re just going to try and figure out — go back to the video from last year and find out what I was doing well at that point and how I was capitalizing on mistakes at that point.”

Mickey Callaway chalked up the loss to a top-notch outing by Stephen Strasburg, who allowed three hits and a walk and struck out nine in 6 2⁄3 innings. While other Mets batters were willing to tip their cap to Strasburg, Nimmo didn’t.

“I think we missed a lot of good pitches,” he said. “I know for me personally, there’s some good pitches that I missed. Strasburg’s always going to go out there and give you his best, but I think we just missed mistakes. Any time you do that, it doesn’t matter who you’re facing; you miss mistakes and they’re going to go ahead and win those battles.”

Nimmo’s day began with a checked-swing strikeout in the first inning and ended with a one-out walk in the eighth, when the Mets were trailing 2-0. But Justin Miller struck out Pete Alonso and Tony Sipp struck out Robinson Cano.

The Mets, who had four hits (all singles), struck out 14 times against five pitchers. The top four in the order went 0-for-14 with seven strikeouts. Cleanup man Michael Conforto struck out three times.

So it wasn’t just Nimmo letting the Mets down Thursday. But he feels the burden of producing after a breakout season in which he had a .263/.404/.483 slash line and 17 homers.

As for the photo on the scoreboard, Nimmo said the Mets’ photographers ask the players for different expressions (including a stern game face). The players don’t know which one is picked until they look at the scoreboard at the home opener — which Nimmo didn’t do.

“I’ll have to check it out Saturday,” he said, smiling.

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