Mets starting pitcher Matt Harvey walks to the dugout against...

Mets starting pitcher Matt Harvey walks to the dugout against the Brewers at Citi Field on April 14, 2018. Credit: Kathleen Malone-Van Dyke

ATLANTA — Matt Harvey is a reliever.

The Mets demoted the former ace to the bullpen Saturday, a move painted by assistant general manager John Ricco as less about turning Harvey into a reliever permanently and more about restoring his confidence and effectiveness so he can be a legitimate starting pitcher again.

Manager Mickey Callaway called it “a big decision.” Harvey, who was unhappy and had hoped to get another start, will be available in relief beginning Tuesday.

“On a scale of 1 to 10, obviously I’m at a 10 with being [ticked] off,” said Harvey, whose measured tone belied his strong words. “But my performance hasn’t been there and I just have to do whatever I have to do to get back in the starting rotation, and that’s right now go to the bullpen and work on some things, get things back to where I need to be, get my [stuff] in order and figure it out.

“I have to suck it up and go out there and do everything I can to get things back in gear. I don’t have to agree with it, but I have to go out there and do the best I can.”

Lefthander Jason Vargas will replace Harvey in the rotation.

Harvey, 29, this month has worked with the lowest fastball velocity of his career (93 mph) and had a 6.00 ERA and 1.43 WHIP in four starts. That includes a six-run, six-inning outing Thursday against the Braves. All of the runs scored in the first three innings, with Harvey recovering to shut Atlanta out for the last three.

Harvey mentioned those “last three innings” nine times in a seven-minute interview.

“Those last three innings the other day, I felt like it clicked,” he said. “I think just being able to go out there and continuously do that and have it work is going to be the most important thing.”

The conversation was not an easy one. Harvey said his piece, about feeling as if the back half of his most recent outing was a breakthrough, but Callaway and pitching coach Dave Eiland had made their decision.

“Matt Harvey has pitched in meaningful games for the Mets in his career, and he’s done some special things,” Callaway said. “I knew it wasn’t going to be the most comfortable conversation. It’s a tough message, but it sounds like he’s going to embrace it and go out there and get the job done.”

Callaway was not sure how he will use Harvey, be it as a long reliever/mop-up man or as a short reliever. Either way, the expectation is that Harvey will return to the rotation at some point.

“It’s inevitable that he’s going to make more starts for us this year. That’s how baseball goes,” Callaway said. “As of right now, we think that indications are that he’s going to go down there and try to be the best Matt Harvey he can be.”

Ricco said the Mets did not consider sending Harvey to the minors, which would have required his approval, because they want him to work with Callaway and Eiland, who have rehabbed starters by sending them to the bullpen in the past.

That background and Harvey’s health are reasons the Mets think this can work.

“He’s feeling good. Then you get to, is this a little bit of a mental thing, a confidence thing?” Ricco said. “One of the things we talk about is getting him into the pen, where he can have success in short spurts, get that confidence back and really let it go and get back to being a guy who can dominate the way he’s shown in the past.”

Harvey — who was drafted in the first round, dominated in the majors at 23, started an All-Star Game and returned from Tommy John surgery to excel in the Mets’ pennant-winning 2015 season — hasn’t been the same since July 2016 surgery to address thoracic outlet syndrome.

“I know when things click that I can be one of the best in baseball, and that’s as a starting pitcher,” Harvey said. “Obviously, I didn’t show that. I have to do everything I can to get back to where I want to be and be as dominant as I have been.”