NEW YORK -- Rain dripped off the brim of Pete Alonso's helmet as he stared in at Albert Abreu, the sixth Yankees pitcher on what, for a variety of reasons, had been a miserable Thursday afternoon for the Mets' first baseman at Citi Field. The previous pitchers had little trouble bottling up Alonso, tempting him to chase offerings above and below the strike zone, and inducing harmless contact on those down the middle.

Considering both his short- and long-term slumps, as well as how much those struggles have impacted the Mets' season, it would have been understandable for Alonso to feel immense pressure heading into his at-bat. Instead, the slugger said, he felt only stillness as he unleashed his best swing on a 98 mph fastball, sending it screaming down the left-field line for a walk-off two-run homer to give the Mets a 9-7 win over the Yankees in 10 innings.

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"This is a valuable lesson," Alonso said. "It doesn't matter what happened. You've just got to stay resilient and keep fighting."

The walk-off homer was the first of Alonso's career, ending a chaotic game that saw the Mets twice come from behind to erase multirun leads, and recover from multiple mistakes -- both physical and mental -- to put themselves in position to win the game. After J.D. Davis hit a game-tying homer off Aroldis Chapman in the bottom of the ninth, the Mets began the 10th with an automatic runner on second base.

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First up was Alonso, whose 0-for-4 line told only a fragment of his story. Dating back further, Alonso was mired in a 1-for-19 slump, or a 4-for-42 dive that had lopped 40 points off his batting average. Last year's National League Rookie of the Year Award winner was still hitting for power, tied for the team lead with seven home runs. But he wasn't doing much else of consequence -- at least not of the positive variety.

Defensively, Alonso was also struggling. In the fifth inning, he committed an error for the third consecutive game when his throw sailed well wide of Jeurys Familia covering the bag. In the seventh, Alonso made a more damaging misplay when he couldn't corral Brett Gardner's bouncer down the first-base line, which went for an RBI double. The Yankees wound up rallying for three runs in the seventh and eighth innings, forcing the Mets to claw their way back into contention -- and then nearly play themselves out of a ninth-inning comeback when pinch-runner Billy Hamilton was thrown out trying to steal third with no outs.

There was, in short, a lot going on. The pulses inside Alonso's brain should have been noisy, messy, distracting. Instead, he found himself "calm and collected … under control and balanced."

"None of the stuff that happened is relevant, or should be relevant," Alonso said. "What matters is that at-bat, because that at-bat is happening now. Whatever happened, all the at-bats that happened before, they don't matter in the moment. In the moment, I've got a job to do. And we have a game to win."

In his mind, Alonso had reason for confidence. For weeks, he has worked diligently in the cage to work out kinks that have developed in his swing. He has tried to quiet his hands as he cocks his bat into position, a tendency that has resulted in frequent late swings. Contrary to popular theory, Alonso is not chasing balls out of the zone more often in 2020. But he is not doing nearly as much damage on strikes, entering Thursday's play with a .554 slugging percentage on balls inside the zone, compared to his .792 mark on those pitches last season.

During a recent cage session, Alonso told Davis that he was trying to whip his bat through the zone more quickly on fastballs, in an effort to barrel them for power.

"Don't try to do it," Davis told him. "Just react. Use those hands. Pull them inside and just rotate with your body."

When Abreu threw a 98 mph fastball on the inner third of the strike zone, Alonso did exactly as instructed. Then he burst into a grin as he rounded third base, keeping it sealed on his face for the final 90 feet of his trot. He nodded his head as he approached his teammates, ripped off his helmet and threw it skyward.

Alonso's earlier calm was gone. And that was a good thing for perhaps the most important member of the Mets' lineup.

"It was a sick ending to the game," Alonso said. "It was extremely fun, but tomorrow's a new day. It's a new series. And it's go-time."