This was supposed to be a breeze. Instead, the breeze that has arrived has chilled the Mets’ bats.

The Mets, who are supposed to be trampling weaker opponents, instead were swept in a three-game series for the first time this season, the final indignity a 6-3 loss to the Cubs at Citi Field on Wednesday night in front of 28,522.

The Mets scored a total of six runs in the three games against a Chicago club that has been out of contention for months. Buck Showalter’s crew next will host the Pirates for four games that seemed easier a few weeks ago.

The Mets are amid a stretch of 16 straight games against sub-.500 opponents, and they have dropped seven of the first 12.

“It was a great opportunity,” Francisco Lindor said about the wasted games. “But at the end of the day, they’re big-league teams. They’re professionals.”

The only positive development around the club is that its nemesis has begun losing, too.

The Mets (89-55) remained a half-game ahead of the Braves, who lost to the Giants and have dropped consecutive series in Seattle and San Francisco.

The Braves have built-in excuses while playing on the West Coast and against competent teams. The Mets could point to injuries — Starling Marte is on the shelf and Max Scherzer missed his second start — but the biggest problems lie with their offense. A six-run deficit in the first inning felt and proved insurmountable.

In a disastrous effort, starter David Peterson was charged with five runs while recording one out in an inning he did not escape. The ditch was dug, and the Mets never got back in the game.

“Just didn’t throw enough strikes,” said Peterson, who likely will be replaced by Scherzer the next turn in the rotation. “This one’s on me. I put us in a hole early, put us in a tough spot.”

The signs of pressing and frustration from the Mets’ offense were everywhere. In the third inning, Darin Ruf chased a breaking ball in the dirt and slowly walked back to a dugout as fans booed him. In the fourth, Pete Alonso flailed at a strike three that bounced and stood at the plate for a few moments, as if refusing to trudge back to the bench. Jeff McNeil grounded out in the seventh and spiked his helmet after touching first base.

Chicago’s Drew Smyly limited the Mets to two runs on four hits through five innings. The Mets could not find the big hit against the Cubs’ bullpen.

“We all want to get it done desperately,” said Lindor, who bounced into an eighth-inning double play to erase a potential rally. “And we will try to do whatever it takes to get it done. We just haven’t come through.”

In the ninth, the Mets had the makings of a threat against Mark Leiter Jr., who drilled McNeil to start the frame. But Eduardo Escobar’s deep drive to right-center was tracked down by Michael Hermosillo, who made a remarkable leaping catch against the wall. Luis Guillorme grounded into a double play to end it.

The Mets’ offense was mostly provided by blasts from Tomas Nido (his second in as many games after being held homer-less for 85 games to start the season) and Alonso (his 35th of the season, in the eighth). They scored another run on a break, when Cubs third baseman Patrick Wisdom whiffed on a Brandon Nimmo chopper to score Escobar from third.

But despite excellent work from the bullpen — the Cubs did not score after the first inning thanks to Trevor Williams, Tommy Hunter, Trevor May, Alex Claudio and Mychal Givens — the Mets never seriously threatened.

Their offense could not make up for Peterson’s disastrous outing.

The lefty first could not find the strike zone and then could not find an out. He walked the bases loaded, struck out Wisdom then surrendered a pair of doubles — one to Yan Gomes, another to P.J. Higgins — for four runs. Showalter had seen enough.

“Kept waiting for him to make some good pitches, but it just snowballed on him,” the manager said after his club lost a season-high third straight game for a fourth time this season

Williams entered and only widened the wound initially, allowing a double to Hermosillo and single to Nelson Velazquez, allowing Chicago to score a touchdown (with no extra point) in the first.

“We’re trying to get to that finish line and have a chance to be the last team standing,” Showalter said. “All those goals are still there for us.”