Few teams have suffered more setbacks this year than the Mets. Already coming off one of the biggest late-season collapses in recent memory, the Mets have given their fans more heartburn this year, thanks to a cavalcade of high-profile injuries — Pedro Martinez, Billy Wagner, Moises Alou, Ryan Church, John Maine, Luis Castillo, and Orlando Hernandez, not to mention plenty of more minor ailments.

The team’s woes seemed to peak in early August. The Mets lost Maine and Wagner to the disabled list, weakening their pitching depth significantly and digging up memories of last year’s bullpen collapses. They’d lost four in a row, falling into third place in the NL East. Worse yet, they’d failed to upgrade their roster at the trade deadline, leaving Mets fans to wonder: Who would save the season?

The team got their answer on August 5, in the opening contest of a three-game series against the Padres. In the 3rd inning of that game, this Met socked a solo homer to tie the game. Then after his team again fell behind, the same Met crushed a three-run homer in the 6th that provided the winning margin. The Shea Stadium crowd of 52,130 chanted the mystery man’s name, demanding a curtain call. Only they weren’t cheering for David Wright, Jose Reyes, or Carlos Beltran.

They were honoring Fernando Tatis.

That 6-5 win launched the Mets on a big run, one that’s seen them win 11 of their past 15 games (heading into las night’s game) and surge into 1st place. If the Mets go on to win the division and redeem themselves after last season’s collapse, they’ll have many players to thank — few more so than the comeback kid, Tatis.

Actually, we’re about a decade late in calling him a kid. Tatis was signed by the Texas Rangers as an amateur free agent at age 17, half a lifetime ago. He soon established himself as a promising third base prospect. After showing flashes of power in his 1997 rookie season, the Rangers traded him to St. Louis as part of a five-player deal in ’98. A year later, Tatis had a huge breakout season, batting .298 AVG/.404 OBP/.553 SLG, clubbing 34 homers, knocking in 107 runs, even stealing 21 bases.

The coup de grace came on April 23, 1999. Facing the Dodgers’ Chan Ho Park with the bases loaded in the third inning, Tatis went deep. The Cardinals’ rally continued, leading to another bases loaded situation for Tatis in the same inning. The result was another grand slam, two in one inning, a feat that had never been matched in baseball history and maybe never will. At age 24, Tatis was a rising star at the height of his powers.

Things quickly went south from there. Tatis put up good numbers the next season, but missed 66 games. He didn’t get along with Manager Tony LaRussa and gained a reputation as a lazy player. That off-season, the Cardinals shipped him to Montreal. Lacking a top third baseman since Tim Wallach’s heyday in the 1980s, the Expos thought they’d landed a 26-year-old gem.

Instead, Tatis showed up for spring training looking sluggish and overweight, complaining about various aches and pains. He played in just 41 games in 2001. The next year he got into 114 games, but hit .228, struggled in the field and generally looked like he was finished. In 2003, he hit just .194, appearing even more sluggish. Frustrated Expos fans took to calling him “Fatis.”

Tatis didn’t play another game in the big leagues for three years. He said the hard turf at Olympic Stadium zapped his knees, while the pessimistic atmosphere surrounding the team sapped his desire to play.

“The hardest thing in baseball for a player is to get hurt,” he said of his years in Montreal. “When you get hurt, that’s it. You’re just not going to be the same player. That’s what happened to me. It felt like it was one thing after another. It was a very frustrating time.”

While sitting out from 2003 to 2006, Tatis stayed at home in the Dominican Republic. His hometown, San Pedro de Macoris, needed to buy land to build a new church. His only chance to earn the money was through a major league comeback, but no one seemed to think he had anything left in the tank. Then before the 2006 season, Tatis got a surprise call from the Baltimore Orioles. Given a chance to raise money for his town and to reignite his desire to play, he accepted. Tatis was a part-time player that year, netting just 56 at-bats before being tossed overboard.

The Mets picked him up, and Tatis played all of last season for the Mets’ Triple-A affiliate in New Orleans. Just after Opening Day, Jerusalem First Church opened in the Dominican. About a month later, when Alou and others hit the DL early in the year, Tatis got what looked like a token call-up. He doubled in his first game May 13, then didn’t play again for a week. After a couple more at-bats in the next couple days, the Mets finally gave him a start on May 23. He went 2-for-3, belting a homer in a 6-5 loss to the Rockies. With nowhere else to turn, the Mets figured they’d let him play every day until he played his way out of a job.

Three months later, they’re still waiting. Tatis is now hitting .294/.359/.489, making him one of the more productive outfielders in the league. With Alou out for the year, Church’s health a question mark and no other reinforcements on the horizon, the Mets are now relying on a 33-year-old converted outfielder who was out of baseball for the better part of five years to help them win the pennant.

There have been plenty of great comeback stories this year, from Josh Hamilton to Kerry Wood to Rick Ankiel. I’ll take the even more unlikely story of Fernando Tatis.

Jonah Keri is a regular contributor to Page 2 and the editor and co-author of “Baseball Between the Numbers.” You can contact him at jonahkeri@gmail.com.