The losses keep piling up in Queens. The punch lines are growing even faster.

With their latest abysmal offensive effort, the Mets collected just three hits, and sealed their four-game home sweep — and sixth straight loss at Citi Field — with Sunday’s 2-0 defeat to the Cubs, while saving their lowest moments for a pair of mental mistakes in the field.

In the midst of a pitchers’ duel between Jon Lester and Steven Matz, a seventh-inning scoreless tie was broken when Javier Baez stole home off an unsuspecting Matz. The Cubs then benefited from Jay Bruce misplaying what became a sacrifice fly, which barely cleared the infield, and handed the Mets (27-30) their ninth loss in their past 11 games.

“The way things have been going, guys have a lot of pressure on themselves, and when that pressure kind of takes over … things kind of fester,” Callaway said. “I think maybe that’s affecting us overall.

“Let’s be honest, this is a tough place to play. New York is tough on players. It’s tough on everybody. If they were in Cleveland or somewhere else, maybe they wouldn’t feel that pressure, but you are playing in New York. We do play in New York. We have passionate fans that want to see a good ballclub out there, so we have to do some things to get over that and make sure that we’re focused every second of the day that we’re out there.”

The pressure shouldn’t be a problem for the players, given most have been here. The first-year manager is one of the few fresh faces to the big city.

Matz started a World Series game at Citi Field. Bruce belted 29 home runs in 103 games with the Mets last season, then signed up for a second stint in Queens.

The issues are far deeper, and far more difficult for the former Indians pitching coach to fathom.

After Matz (2-4) extended his scoreless streak to 15 innings, and matched Lester with six scoreless frames, the Mets lefty surrendered back-to-back singles to Baez and Willson Contreras, putting runners at the corners to start the seventh.

With his back toward third, Matz softly threw to first without realizing Baez had already started sprinting home, giving the Cubs a lead that was insurmountable for an offense that would struggle in Binghamton right now.

“Honestly, it was completely out of my mind,” Matz said. “That’s my fault. I should’ve been more aware, especially with a guy like Baez, a really aggressive guy on third base.

“I’m never paying attention to the runner at third base. I’m out of my stretch, so I don’t think he’s gonna steal home on me, and honestly it just caught me off guard. Will I in the future now? Yeah, I’ll be a little more mindful of that throw over to first, and just kind of look at him before I step on the mound, and make sure he’s not shuffling down the line.”

The next indefensible error came before the inning ended.

With Contreras at third, Ben Zobrist hit a shallow pop up, on which right fielder Jay Bruce failed to call off backtracking second baseman Luis Guillorme, whose weak throw home was late.

“It was very, very, very shallow, and I think that’s why I wasn’t overly concerned with catching it,” Bruce said. “It drifted back more than either of us thought. Obviously, hindsight being what it is, I catch it, and he doesn’t run. … It looks terrible. I have to be better.”

Though Lester (6-2) was sharp for seven innings, most southpaws capable of throwing 60 feet, 6 inches, would have fared well against the majors’ worst offense against left-handed pitching.

Lester even provided an early opportunity by opening with back-to-back walks, but he followed with three straight strikeouts, and didn’t allow the first hit until a two-out single by Kevin Plawecki in the sixth.

That inning ended with Adrian Gonzalez grounding out with the bases loaded. The first baseman followed with a crowd-killing ninth inning double play.

Over the past 24 innings, the Mets have scored just one run. Over the Cubs’ first four-game sweep in Queens since 1991, the Mets scored six runs.

The offense was as awful as it’s ever looked — but still far from the biggest issue on the manager’s mind.

“It’s frustrating. You’re giving them the game instead of them winning the game from you. That’s always hard to accept,” Callaway said. “I think it’s focus. That has to be what it is. Been playing the game a long time, all these guys, and if you’re not doing the things you’ve learned for years and years, and done for years and years, then to me, that’s probably a lack of focus at that point.”