Edwin Diaz #39 of the Mets looks on after surrendering...

Edwin Diaz #39 of the Mets looks on after surrendering a ninth inning home run against Jesse Winker #33 of the Cincinnati Reds at Citi Field on Monday, Apr. 29, 2019. Credit: Jim McIsaac

In the Mets’ 5-4 loss to the Reds on a chilly, windy, occasionally rainy and generally forgettable Monday night at a nearly empty Citi Field, the difference was the proverbial One Bad Inning and One Bad Pitch.

The bad pitch came at the end, from Edwin Diaz to Jesse Winker in the top of the ninth. It was a fastball meant to be inside that instead ended up over the heart of the plate, and Winker crushed it 415 feet to right-center for the go-ahead home run.

“It was just that one pitch that I made a mistake on,” said Diaz, whose ERA rose to 1.54. “I felt great in the bullpen, and once I got out there, I felt good. But he just caught me.”

The bad inning came near the beginning, when Zack Wheeler walked two batters to begin the second and allowed several soft batted balls that found holes. Jose Iglesias sneaked an RBI double down the first-base line and Jose Peraza did the same down the leftfield line to key the four-run frame.

“It’s a frustrating one just because of that inning,” Wheeler said. “Other than that, I think it went well, but the second inning, I was a little off out of the stretch and obviously walked the first two guys. Walks will kill you every time.”

Altogether, it meant the Mets dropped to 14-14, flirting again with a losing record, which they haven’t had all season. They will look to stave off that fate Tuesday as Jason Vargas (7.20 ERA) gets the ball opposite Luis Castillo (1.23 ERA).

Diaz getting dinged was noteworthy because of its rarity. The righthander, who was pitching for the third day in a row for the first time since August, historically has been particularly effective against lefthanded hitters.

This season, lefties were 0-for-15 with 10 strikeouts against Diaz before Winker went deep. That included Joey Votto, a former NL MVP and a six-time All-Star, who flied out to center to begin the ninth.

In 2018, lefties hit .144 with one home run against Diaz. (The Dodgers’ Max Muncy burned him for a blown save in August.)

Then came the one bad pitch, which turned into a career-high eighth homer for Winker.

“And that kid can hit a little bit,” Mets manager Mickey Callaway said. “He’s probably their best hitter, especially when Votto’s not going great.

“[Diaz] threw the ball really good. He just made one bad pitch and they made him pay. Sometimes they pop those up or mis-hit them or swing through them. That guy didn’t tonight. [Diaz] had a real crisp, clean inning. Breaking ball was good, fastball was good. Just one bad pitch.”

Or as catcher Wilson Ramos put it: “That was a right-down-the-middle pitch. Nobody’s perfect in this game.”

Wheeler (six innings, four runs) was good outside of his one bad inning. How unusual of a sequence was that? He allowed as many as three runs in an inning just twice in his first 30 frames this season. And the Reds have averaged less than four runs per game this year.

Reds starter Tanner Roark gifted the Mets a tying two-run rally in the fourth. With two outs, Roark had Juan Lagares in an 0-and-2 count before losing the strike zone. Lagares walked and Wheeler dunked a single into center. Jeff McNeil drew a walk to load the bases and Pete Alonso walked to force in a run, ending the night for Roark, who was charged with four runs in 3 2⁄3 innings.

Reliever Wandy Peralta walked his first batter, Brandon Nimmo, on four pitches to tie the score. And that’s the way it stayed until Diaz’s mistake.

“I’m ready for the highs and lows of the game,” he said. “I’ve pitched well, but today I [can accept] the loss because I don’t think I’m going to have many more this season.”