NASHVILLE, Tenn. — The day began with the Mets awash in optimism about their chances of signing their No. 1 target this offseason: Ben Zobrist.

But after an evening of twists and turns, it ended in bitter disappointment.

The Cubs made a last-minute push on Tuesday to sign Zobrist to a four-year, $56-million deal pending a physical, sources confirmed. Now, as they did at the trade deadline, the NL champion Mets must regroup from a major setback.

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“It’s disappointing, I’ll be honest,” assistant general manager John Ricco said. “He’s a guy we thought fit very well for us.”

As the day played out, the Mets’ confidence eroded with the emergence of the Cubs as a serious suitor, a position solidified because they were closing in on a trade with the Yankees.

The Cubs long had been enamored with Zobrist, according to an industry source, though he didn’t have a clear landing spot in the infield. But when the Cubs’ trade of Starlin Castro to the Yankees came together, Zobrist’s situation changed.

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“I don’t think this was about money,” said Ricco, who heard directly from Zobrist about his decision. “It was about him finding a place that fit. I think he liked a lot about what we are. But . . . he has some history with the manager in Chicago, it’s a little closer to home for him, so he made that decision and we’ll move on.”

Ricco declined to divulge the Mets’ offer, though it was reportedly comparable to the one submitted by the Cubs.

“I thanked him,” said Ricco, who heard from Zobrist at a dinner in which general manager Sandy Alderson was honored as Baseball America’s executive of the year. “He came in and met with us. We’ll move on and we’ll be all right.”

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Throughout the courtship, the Mets had gone out of their way to make clear that Zobrist was their top target. They had long prepared themselves to offer a fourth guaranteed year.

After winning the pennant for the first time since 2000, the Mets sold themselves as a franchise on the rise, an attractive quality because Zobrist prioritized playing for a winner. The Mets also insisted that Zobrist would play mostly at second base, another appealing selling point.

But the Cubs held a trump card: Joe Maddon. Also, Chicago is closer than New York is to Zobrist’s home in Nashville.

Zobrist was a key cog on the Rays teams that under Maddon’s guidance became a steady threat in the AL East, a club that won the pennant in 2008. That connection — and the trade of the middle infielder Castro to the Yankees — appears to have undermined what has been an aggressive pursuit.

Castro, incidentally, had been connected in trade rumblings with the Mets off and on for the last few years. But Ricco refused to divulge whether the Mets were ever serious players for him.

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“We’ve had a lot of discussions with the Cubs over time and I’m not going to comment about any individual players,” he said.

The Mets saw Zobrist as a good fit because of his versatility and plate discipline. He would have represented a defensive upgrade over Daniel Murphy.

But now, as they did when the Carlos Gomez fell through in July, leading to a transformative trade for Yoenis Cespedes, the Mets must rebound. Second base remains a hole.

According to sources, the Mets have not zeroed in on any single fallback option.

While the door remains open for a reunion with the free agent Murphy — Ricco acknowledged the Mets have maintained contact with his reps — his market is expected to pick up now that Zobrist is off the board. And the Mets consistently been cool to the idea of a long-term deal with Murphy.

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The Mets have shown interest in Pirates second baseman Neil Walker, according to a source, but are not interested in Dodgers’ free agent Howie Kendrick.

The Mets could also bank on 21-year-old prospect Dilson Herrera to play second base and get more aggressive in other areas, such as landing a centerfielder.

Of course, the Mets also could attempt to find another middle infielder, whether via free agency or in a trade.

“I think both avenues are open to us,” Ricco said. “We’ll regroup and decide which way we’re going to go. But we knew this was a possibility all along so it’s not a complete shock.”