NEW YORK -- Shortly after the Mets named Mickey Callaway manager in late 2017, he outlined his philosophy on bullpen usage at that year’s Winter Meetings. In short, Callaway said he did not want to lock any pitcher into the closer’s job, preferring to keep roles fluid and “pitch guys when it makes sense.”

For the most part, though, Callaway has spent his tenure relying on traditional bullpen roles. He employed a set closer most of last season and, after the Mets acquired Edwin Díaz this winter, Callaway and the front office drew up strict rules for Diaz’s usage. As recently as July 30 in Chicago, Callaway referenced Diaz as his closer -- as his primary ninth-inning option -- in any save situation.

Now, though, those rules appear to be softening, if not outright changing. When a save situation surfaced in Saturday’s 4-3 win over the Nationals, Callaway stuck with Seth Lugo, who had pitched the eighth inning, rather than turn to Diaz. The following morning, Callaway indicated Lugo will see regular save opportunities going forward, even if he hasn’t supplanted Diaz as the closer in name.

“I think you always have to be open for adjustments,” Callaway said. “The season is going to change. Guys are going to be effective at times, not effective at times. At this point, the sample sizes aren’t that small anymore. I believe that guys have earned a right to do something until they haven’t.”

Lugo has not just been the Mets’ most effective reliever, but one of the most effective in the entire Major Leagues. Since April 22, he owns a 1.80 ERA with 59 strikeouts and nine walks. Diaz, over that same stretch, has a 6.19 ERA with six loses and five blown saves.

But the Mets are not naming Lugo their closer because they want to be flexible about his usage. Valuing Lugo’s ability to log four to six outs in a game with regularity, the Mets are committing to using him in the ninth inning of games he’s already entered in the eighth. Those multi-inning outings, however, typically leave Lugo unavailable the next day. That opens up plenty of chances for Diaz to save games, too.

It is the exact type of strategy Callaway outlined a year and a half ago at the Winter Meetings, but hasn’t truly implemented until now.

“I think we have to do that at this point, and not just when it comes to that role,” Callaway said. “Every role. … It takes selflessness to do special things, and that’s what these guys are doing right now.”