CHICAGO -- Following the firing of pitching coach Dave Eiland and bullpen coach Chuck Hernandez prior to Thursday’s series opener in Chicago, the message from Mets general manager Brodie Van Wagenen to the team’s pitching staff was pretty clear.

“When we assessed the team over the first two months of the season, in particular, the last several weeks, we felt that the bullpen performance had a lot of room to improve and that is the root of this move,” he said.

• Box score

Unfortunately, the bullpen woes continued as New York saw another late lead fall by the wayside in Sunday’s 5-3 loss to the Cubs at Wrigley Field.

Things lined up well for manager Mickey Callaway going into the bottom of the eighth inning in Sunday’s series finale. The Mets had scored three runs off Cole Hamels, who had been tough coming into Sunday’s start, Jacob deGrom pitched well as usual and the team’s two best bullpen options were ready and available.

New York’s most-reliable setup man, Seth Lugo, had to work as Chicago forced him to throw high-stress pitches for multiple innings. Lugo avoided trouble in the seventh, but on a hot day at Wrigley Field and each at-bat more draining than the last, the Cubs turned up the heat a little more on Lugo.

Kyle Schwarber started the eighth inning with a six-pitch AB that ended in a base hit. Kris Bryant followed with an eight-pitch AB, ending in a sharp lineout to center, and Anthony Rizzo worked a five-pitch walk.

Lugo’s usually sharp stuff wasn’t there, and the Cubs’ hitters could see it like sharks sensing blood in the water.

“It was kind of humid, but that’s no excuse,” Lugo said. “I don’t know. I just wasn’t executing my pitches.”

Despite lacking his best stuff, Lugo got free-swinging Javier Baez down into an 0-2 count, but what’s been true for the Mets’ bullpen all season is that what can go wrong, usually does.

The right-hander hung a slider and Baez made him pay, sending a no-doubt three-run shot into the right-field bleachers to give the Cubs a 5-3 lead.

"I was trying to get a slider off the plate,” Lugo said. “I kind of got under it and it backed up. Pretty much ended up right in his bat path."

“I wasn't looking for a fastball there, because he did throw me one and it was out of the zone,” Baez said. “So I kind of knew that he wasn't going to throw in the zone. It was just kind of hanging a little bit and I just got good barrel on it.”

The Mets have now blown a National League-leading 17 saves this season and with Lugo clearly struggling in the eighth, having Edwin Diaz rested and available to come in for the five-out save seemed to be the next move.

“Not for five outs,” Callaway said. “He would have been available in the ninth if we had gotten to it. Lugo was going to face Baez either way.”

Callaway’s decision not to use Diaz stems from the team’s predetermined plan for its closer, but the manager added that the team could have possibly used Diaz for four outs had the situation called for it.

“We’re not going to use him for five outs. That’s the bottom line,” Callaway said. “We’ve said it all along that Diaz is our closer and we’re going to make sure he stays in that comfort zone.”

The eighth-inning meltdown soured what was shaping up to be a very good weekend for the Mets. The offense showed up, outhomering the Cubs 9-3 in the series; the starting pitching gave quality innings, minus Thursday’s rough outing by spot starter Walker Lockett; yet the Mets left Chicago with a series split instead of a series win.

“It’s frustrating, but we gotta flush it,” said Pete Alonso, who set the Mets rookie record for home runs in the loss. “We got a big series coming up in Philly, a divisional rival. We have to turn the page. Play good ball and go from there.”

New York’s bullpen ERA now sits at an NL-worst 5.16, and with the front office showing it will make moves if things aren’t working, more changes may be the Mets’ new reality in the coming weeks.