Youngster continues to struggle in 1st frame

Robert Gsellman has struggled out of the gate all season, but Wednesday he took his first-inning woes to the next level — and took the Mets right out of the game.

The young right-hander had his worst start of the year, coughing up five runs in the first inning and never giving the Mets a chance in an 8-2 loss to Atlanta, their fifth straight defeat and ninth in 10 games.

“I didn’t think his stuff was as crisp as we’ve seen it. Obviously the velocity was down a few ticks from what it normally is, and he’s usually got better command of his offspeed pitches,’’ Terry Collins said. “In the first inning, he didn’t have either going. He fell behind in the counts, and when you fall behind in the count in the big leagues you’re going to get in trouble.

“He’s a guy that really does try to compete, and after the first inning I think he gets a better feel for his sinker. It hasn’t been as sharp as we’ve seen it. Hopefully there’s nothing wrong physically, but we’ve seen better stuff. Maybe you just write this one off to a bad night that we certainly got way behind early which really hurt us when you’re facing a guy you don’t hit.”

Strip away a pitcher’s stuff, command and velocity, and there’s not much left. And that’s about how helpless Gsellman (0-2) looked in the first, undone by his own throwing error and capped by Tyler Flowers’ bases-clearing double. In all he gave up six runs — five earned — in just four-plus innings. The 10 hits and three walks he gave up were both career highs.

But the damage has mostly taken place in the first frame. His first-inning ERA ballooned to 22.50, while he has pitched to a solid 2.55 in innings other than the first.

“I’m just leaving the ball up early and they get their runs in the first inning. I just need to go out there with the right mechanics in the first inning and shut them down from the get-go. [I’m] just flying open and the ball’s running side-to-side instead of up-and-down,” said Gsellman, who attributed his dip in velocity to being tight and not staying loose.

“The first inning’s been a big struggle. I just need to [be ready] for the game from the beginning and get guys out instead of walk people in the first inning and give up hits. [I need to] put up zeroes, give the ballclub a chance to win.”

He didn’t do that Wednesday.