LAKELAND, Fla. — Among the many candidates for the Mets’ Opening Day bullpen is last year’s closer at Triple-A Las Vegas, righthanded slider specialist Paul Sewald.

Sewald, 26, began spring training as a long shot, but a 1.29 ERA in five exhibition appearances, including two perfect innings against the Nationals on Saturday, has put him squarely on manager Terry Collins’ radar.

“He’s a strike-thrower,” Collins said. “We saw it last year. We saw it during the season. Ultimately, when we get down towards the end, when we decide where we are standing in our bullpen, where we perhaps need a guy who can give you some innings, he might be in that mix.”

At the moment, there are four pitchers in the Opening Day bullpen for sure: Addison Reed, Fernando Salas, Hansel Robles and Jerry Blevins.

Closer Jeurys Familia is expected to be suspended for the start of the season for violating baseball’s policy on domestic violence. The length of the suspension has not been announced. Familia is pitching for the Dominican Republic in the World Baseball Classic.

Reed, who will fill in as the closer, opened the Grapefruit League season with three scoreless outings. In his last three, he has given up nine runs in three innings, including six in two-thirds of an inning Friday. But Collins said he is not worried about the veteran righthander, who has an exhibition ERA of 16.20.

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That leaves three spots open. Collins mentioned eight names, including No. 5 starter candidates Seth Lugo, Robert Gsellman and Zack Wheeler. Collins also ticked off the names of righthanders Sewald and Rafael Montero and lefthanders Josh Edgin, Josh Smoker and Tom Gorzelanny.

“There’s a lot of candidates,” Collins said. “We’re just going to keep pitching ’em.”

Montero allowed two inherited runners to score in 1 2⁄3 innings and Edgin threw a scoreless inning in Sunday’s 4-3 loss to the Tigers.

Collins didn’t mention Erik Goeddel, who is on the 40-man roster but has an ERA of 11.25 in four exhibition outings. Sewald is not on the 40-man roster. He would have to be added if he were to make the team.

“At the end of the day, there’s three weeks left in camp, so a lot could happen, good or bad,” Sewald said. “For me, I’m not worried about what Terry’s going to say, what the front office is going to say. I’m just worried about going out there and pitching the best I can when they call my name.”

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Sewald, a Las Vegas native, went 5-3 with a 3.29 ERA and 19 saves in 56 games for the 51s last season. He has started an exhibition game and went two innings Saturday, which indicates the Mets are looking at him for a more-than-one-inning role.

“I definitely feel like I’m throwing well,” he said. “Real smooth with my delivery. My best pitch is my slider, and that’s always the last thing to come in spring training. But I felt like [Saturday] was the best it had been all spring training, so that was a positive sign.”

Another positive sign for Sewald would be breaking camp with the Mets.

“I have never been to Citi Field,” he said. “I’ve been to Shea Stadium. First time I’ll be at Citi Field hopefully will be in a uniform.”

Notes & quotes: Juan Lagares was supposed to play but was scratched with a stiff back before the Mets left for Lakeland . . . Kevin Plawecki went 1-for-3 as the DH in his first game since suffering a left knee contusion in a home-plate collision Feb. 25. Collins said Plawecki’s knee stiffened up enough that he was unable to stay in for a fourth at-bat. Both players are day-to-day.