NEW YORK — Bud Harrelson, the scrappy and sure-handed shortstop who fought Pete Rose on the field during a playoff game and helped the New York Mets win an astonishing championship, died early Thursday morning. He was 79.

The Mets said Thursday morning that Harrelson died at a hospice house in East Northport, New York, after a long battle with Alzheimer’s. He was diagnosed in 2016 and publicly shared his struggle two years later, hoping he and his family could help others afflicted.

Throughout his health ordeal, Harrelson stayed involved with his professional pride and joy. He was part-owner of the Long Island Ducks, an independent minor league team located minutes from his home. He called his decades of work with the club — which he was instrumental in starting and running — his greatest achievement in baseball.

The team said Harrelson’s family was planning a celebration of his life for a later date.

During a major league career that lasted from 1965 to ’80, the light-hitting Harrelson was selected to two All-Star Games and won a Gold Glove. Known to family and teammates as Buddy, he spent his first 13 seasons with New York and was the only man in a Mets uniform for both their World Series titles.

The first came as the infield anchor of the 1969 Miracle Mets, the other as the club’s third-base coach in 1986.

In one of the most famous scenes in baseball history, it was a euphoric Harrelson who waved home Ray Knight with the winning run on Bill Buckner’s error in Game 6 of the ’86 World Series against Boston.

Harrelson also managed the Mets for nearly two seasons, guiding them to a second-place NL East finish in 1990 after taking over in late May. He was inducted into the team’s Hall of Fame in 1986, joining Rusty Staub as the first two players honored.

“It was easy to see why the ’69 guys loved him. He was great on defense and he was tough,” Mets broadcaster Ron Darling, who pitched for the club from 1983 to ’91, told the New York Post in 2018.

In Game 3 of the 1973 NL Championship Series between the Mets and Cincinnati Reds, Rose slid hard into Harrelson at second base on a double play. The two ended up toe-to-toe and then wrestling in the infield dirt at Shea Stadium, triggering a wild, bench-clearing brawl that spilled into the outfield.

Outweighed by more than 30 pounds, the scrawny, gritty Harrelson got the worst of it.

But he didn’t back down.

“I have no regrets about going at it with Rose. I did what I had to do to protect myself, and Pete did what he thought he had to do to try to motivate his team,” Harrelson wrote in his 2012 memoir, “Turning Two: My Journey to the Top of the World and Back with the New York Mets” co-authored by Phil Pepe. “We fought and that was the end of it.”

Sort of.

The game was held up as irate fans hurled objects at Rose, and the Reds were pulled off the field by manager Sparky Anderson until order was restored. Mets skipper Yogi Berra and players including Willie Mays and Tom Seaver went out to left field to calm the crowd.

Cincinnati players apparently were peeved about a comment from Harrelson after Game 2. Making light of his own shortcomings, Harrelson said Mets pitcher Jon Matlack “made the Big Red Machine look like me hitting” after the left-hander tossed a two-hit shutout.

“I didn’t think it was all that bad. I was kind of putting myself down a little bit, but I was also putting them down,” Harrelson said. “Then I heard that they were going to come after me and all that, so I figured that was it right there. And when Pete hit me after I’d already thrown the ball, I got mad. And we had the little match. He just kind of lifted me up, laid me down to sleep and it was all over.”

Harrelson later wrote that Charlie Hustle caught him with “a cheap shot.” But the former shortstop would also joke about the fracas, often saying: “I hit him with my best punch. I hit him right in the fist with my eye.”

The two became teammates in Philadelphia years later and when their playing days were long over, Harrelson said Rose, baseball’s career hits leader, signed a photo of the fight for him and wrote, “Thanks for making me famous.”

Harrelson later managed Rose’s son with the Ducks, and the elder Rose even attended a couple of games, Harrelson said.

Harrelson was traded to the Phillies in 1978 and spent two years with them before playing his final season for the Texas Rangers. A switch-hitter, he finished his career with a .236 batting average and .616 OPS. He hit seven home runs — never more than one in a season — and stole 127 bases, including a career-high 28 for the Mets in 1971.

Despite his lack of power, Harrelson could be pesky at the plate. He drew 95 walks in 1970 and was always a good bunter. He batted .333 lifetime (20-for-60) against Hall of Famer Bob Gibson, with 14 walks and just three strikeouts for a .459 on-base percentage.

“I have always said I’ll take God to three-and-two and take my chances. I might foul two off before He gave me ball four,” Harrelson wrote.

Harrelson came off the bench in the 1970 All-Star Game in Cincinnati, getting two hits and scoring twice. He was the National League’s starting shortstop the following season at Tiger Stadium and won his only Gold Glove that year.

Harrelson went 3-for-17 (.176) with three walks when the Mets beat heavily favored Baltimore in the 1969 World Series. He had a .379 on-base percentage during a seven-game loss to Oakland in the ’73 Series, after New York upset Cincinnati in the playoffs.

As manager of the Mets from 1990 to ’91, Harrelson compiled a 145-129 record.

Derrel McKinley “Bud” Harrelson was born in Niles, California, on D-Day: June 6, 1944. He went to college at San Francisco State and signed with the Mets in June 1963 for $13,500 even though the New York Yankees offered $3,000 more.

Harrelson said he was a little intimidated by the Yankees’ storied history and worried he might get stuck in the minors with them. He figured the Mets, an expansion franchise in 1962, might provide a faster path to the majors.

Early in his pro career with the struggling club, he tried switch-hitting at Casey Stengel’s suggestion and stuck with it.

In 1972, Harrelson authored an instructional book titled “How to Play Better Baseball.”

After his diagnosis, Harrelson joined the board of directors of Alzheimer’s Association Long Island and worked with his family to raise awareness. He still made it out to Ducks games, eagerly greeting fans as a goodwill ambassador even if he couldn’t throw batting practice or coach first base anymore.

“I feel like I’m home when I’m there. I’m with the people I love,” Harrelson told the Post.

“I want people to know you can live with [Alzheimer’s] and that a lot of people have it,” he said. “It could be worse.”

Despite his condition, Harrelson was at Citi Field in 2019 for the Mets’ 50th anniversary celebration of their 1969 championship. Tom Seaver, his good friend and former roommate, did not attend after the Hall of Fame pitcher was diagnosed with dementia.