NEW YORK — The changeup tumbled toward home plate. Bryce Harper’s eyes grew wide. A borough held its breath. The game, the series and the magnificent seasons of two teams teetered in the balance.

For Mets hurler Sean Manaea, it was a particularly audacious pitch selection, given the circumstances. His club was up a pair of runs in the sixth inning of an eventual 7-2 victory in NLDS Game 3. Two Phillies hovered on base. There were no outs. The most imposing playoff performer in MLB history waited 60 feet, 6 inches away.

Both men knew that one bad pitch, one big swing, and the trajectory of this scintillating series would be rerouted once more.

Changeups rely on trickery. Movement helps, too, but for the change-of-pace offering to succeed, a pitcher must mimic the arm speed of a fastball. If the pitch works, the hitter incorrectly reads a heater out of the hand and prematurely begins to coil forward, his swing passing through the zone well before the baseball.

But there is ample risk involved. A lifeless changeup is essentially a batting practice fastball, the type sluggers such as Harper turn into souvenirs. That is largely why the Phillies’ first baseman, a left-handed swinger, saw only five first-pitch changeups from left-handed pitchers in the regular season. Wrong-handers tend to attack Harper with a barrage of fastballs and sliders.

Manaea threw only one left-on-left changeup after the All-Star break this year. Uncoincidentally, that was also against Harper.

Before this wave of traffic, Manaea had been cruising. A few hard-hit balls but nothing frightening. A pair of solo home runs from Jesse Winker and Pete Alonso had given the Mets a sturdy 2-0 lead. Phillies hitters, struggling to adjust to the southpaw’s helter-skelter arm angle, managed only two hits through five innings.

But a pair of walks from Manaea to begin the sixth heightened the stakes.

That’s because opposite the Samoan southpaw stood Harper, the epitome of October clutch, the owner of the highest playoff OPS in MLB history. Mets pitching coach Jeremy Hefner, understanding the moment, bounced out of the dugout for what would prove to be a critical mound visit.

Two days earlier, Harper had, for the umpteenth time in his storied career, reminded the baseball world of his postseason bona fides. The Mets were the unlucky victims as Harper’s defibrillating two-run moon shot in Game 2 propelled the Phillies to an unforgettable victory that evened the series.

As Hefner, Manaea and catcher Francisco Alvarez consulted with one another, mouths covered, heads nodding intensely, their target prowled by home plate. Harper retightened his bright red batting gloves a few times before reaching down to level out a clod of dirt in the left-handed batter’s box. A half-minute later, Hefner departed, his contribution made, a critical piece of advice shared: Manaea would throw Harper a first-pitch changeup.

The Mets returned to their positions. Harper dug his cleats into the manicured clay. An eager crowd rose to its feet. Manaea, his cheeks red from exertion, glistened with sweat beneath the stadium lights.

He took a deep breath and readied for battle.

This was not the first time these two had faced off in October.

Before Manaea resurrected his career with the San Francisco Giants and New York Mets, he was a disappointing emergency option for the 2022 San Diego Padres. In Game 4 of that year’s NLCS in Philadelphia, Manaea was summoned to protect a 6-4 Padres lead. Instead, he was bombarded into oblivion. The Phillies pounded him for five runs over just an inning and a third. Harper landed the knockout blow, a go-ahead RBI double on a zipless sinker.

After Tuesday’s game, Manaea referred to that day as “rock-bottom.”

But the silver lining of failure is the opportunity for change, and Manaea used that gloomy night in Philly to turn things around. He immediately emailed Driveline, the high-tech private pitching development company, asking for help. It was the first step on his journey back to dominance. That winter led to an encouraging 2023 with San Francisco, during which he tossed more than 115 solid innings.

But this year, in his first season with New York, Manaea has blossomed into the best pitcher for the sport’s most delightful traveling circus. He altered his release point and pitch mix in the middle of the season, to great success. The sheer wildness of the 2024 Mets has somewhat overshadowed Manaea’s brilliant second half, but over his final 20 starts, the left-hander posted a 3.05 ERA in 121 innings. He will opt out of his contract this winter to become a free agent and rake in a well-earned payday.

All of that was far from Manaea’s mind on Monday. Especially once Harper, his sights set on bludgeoning a baseball into the Long Island Sound, swung and missed at Manaea’s first-pitch changeup.

Strike one.

At that point, neither the at-bat nor the game had been won. But that changeup altered the complexion of the showdown and, with it, the inning and the game.

“That pitch changed the whole at-bat,” Alvarez, the catcher, told Yahoo Sports after the game. Hefner, the pitching coach, confirmed that the trio had agreed on the plan of attack during the mound visit.

By throwing Harper a changeup, Manaea threw a wrench into his opponent’s approach. Harper suddenly had to think about three pitches instead of two. That discomfort and indecision bubbled up. Harper whiffed at the next two offerings from Manaea, both sweepers off the plate.

Strike two. Strike three.

The next batter, Nick Castellanos, lined into a double play to end the inning and the threat. Manaea returned to pitch a scoreless seventh. He came back out for the eighth but was removed after allowing a leadoff infield single to Edmundo Sosa. Mets manager Carlos Mendoza made the slow trudge to the mound. Citi Field, which thoroughly enjoyed its first playoff game this October, rose to its feet. Manaea, who finished the evening with a sparkling line — 7 IP, 1 ER, 3 H, 6 K — tipped his cap to the adoring crowd.

“The ups and downs and through the hardships, that’s what makes games like this mean so much,” a grateful Manaea said after the game. “It’s a part of the work that I’ve been able to do — not just myself, the whole team. Everybody I’ve been working with just put so much time and effort into it. To have results like this is an unbelievable feeling.”

Manaea said he took no extra joy in avenging his 2022 performance against the Phillies. The opponent, to him, was less important than the results, less important than the journey. He has undergone so much change that he didn’t even watch his previous playoff matchup with Harper. It wasn’t a relevant data point.

“The thing about it, you know, I’m not the same pitcher I was then,” he said.

On Wednesday, Manaea will watch from the dugout as his Mets teammates try to close out the series against Philadelphia. A win will send this blue and orange parade to the franchise’s first NLCS since 2015 and give Manaea, his star rising with each sparkling start, even more opportunities for change and changeups.