PITTSBURGH — Seth Lugo was named NL Reliever of the Month on Saturday. Could a shift in job responsibilities be far behind?

Following the Mets’ 7-5 victory over the Pirates, manager Mickey Callaway indicated he will consider Lugo for the closer’s role, as Edwin Diaz continues to struggle. The disappointing Diaz surrendered a two-run homer in the ninth inning to Starling Marte and saw his ERA rise to 5.44. Lugo pitched a scoreless eighth after going all of July without allowing an earned run.

“I don’t think anybody is locked into roles,” Callaway said. “We’re going to do whatever it takes to win, based on usage and things like that.”

Lugo wishes he could say winning Reliever of the Month was a goal, except he didn’t realize the award existed until a Mets public relations official informed him he had won it for July.

“I wouldn’t have heard about it because I’ve never been around a guy who has won it,” the Mets right-hander said, noting that Billy Wagner (July 2007) was the last previous winner from the team.

The Mets have needed such a standout performance in a bullpen that has largely been besieged by underperformance (see Diaz and Jeurys Familia) and injury (see Justin Wilson) for most of the season.

Lugo has encountered one slump — in late June he blew the save in three straight appearances — but otherwise has been close to untouchable.

“I’ve had my ups and downs, but I feel pretty confident in the way the season has gone, my approach to pitching, so I am happy where I’m at right now,” Lugo said.

“I think it’s a matter of staying where I’m at now and my approach to the game, my thought process. I am just going day to day and not thinking about the bigger picture. I’m just thinking about the pitch I am throwing right now and not thinking about three pitchers later or the next batter or the next inning. That is what has really happened in the last month.”

J.D. Davis’ shift to a full-time player is going about as smoothly as the Mets could have hoped.

With Dominic Smith on the injured list with a stress reaction in his left foot (he will remain in a walking boot until at least late August), Davis over the past week has become the team’s primary left fielder. Callaway can’t complain about the results.

“He’s played an adequate left field,” Callaway said. “There’s some balls, just like Dom, they are not going to run down balls in the gap all the time, but he’s making the plays that he should. He’s showing a great arm and we all knew that coming in, so I think he’s doing a tremendous job.”

Callaway has urged Davis to keep him informed if he needs a day off on occasion because of the increased workload. But the Mets also want his bat in the lineup as much as possible: Davis entered play with a .977 OPS since June 4.

Overall this season, he had an .862 OPS against lefties. Against righties he had an .835 OPS.

“We knew he was a great hitter,” Callaway said. “I think he just needed that chance at the major league level. He’s always performed in the minor leagues, limited time in the major leagues before this year, he’s shown some good signs.”

Jeff McNeil was on the bench for a rest — moving Amed Rosario to the leadoff spot and Juan Lagares into the lineup in center field. Callaway indicated he may use McNeil for both games of Monday’s doubleheader against the Marlins and wanted to ensure he had a day off first. Callaway said his Sunday and Tuesday lineups will be constructed based on his plan for Monday.

The Mets signed left-handed reliever Donnie Hart off waivers from the Brewers and assigned him to Triple-A Syracuse. … Jacob Rhame was recalled from Syracuse and Tyler Bashlor optioned.