Long before he became the greatest closer of all time, Mariano Rivera was just another lost rookie in the big city.

That’s when Joe Fosina, the re-conditioner of Yankees uniforms since 1978, essentially the team’s tailor, offered a helping hand.

“Mariano had just gotten called up and he didn’t speak English, but he had an address on a piece of paper,’’ Fosina said of that day in 1995. “The address was in Eastchester and I lived in New Rochelle, the next town over. The equipment guy asked me to go down to the cab and explain how to get there because he knew I lived close by and I said, ‘No, I’ll drive him.’

“That day we had a language barrier, but Mo wanted my phone number. I gave it to him and the next day he called and said he needed a ride to Yankee Stadium,’’ Fosina, 76, recalled.

“That first week I drove him back and forth to the Stadium and then I found an apartment for him in New Rochelle, a nicer place, because he was there with his wife, Clara, and their 2-year-old.”

From that thread of kindness, a lasting friendship developed; a friendship as strong as the interlocking “NY” on those classic uniforms Fosina cares for on a daily basis.

Rivera and his family found solace in New Rochelle in backyard barbecues at the Fosina home with Joe and his wife, Mickie, their five sons and one daughter.

The two families have remained close for 19 years.

“Not only does Mo know all the family, he knows all the grandkids, I got 15 of them,’’ Fosina said proudly.

Rivera is deeply appreciative of the friendship.

“Joe has been like family to me,’’ Rivera told The Post. “From that first day, we clicked. He helped me in amazing ways, giving me rides, back and forth, teaching me the ways of New York and everything about the Stadium. Amazing, amazing.

“Joe, his wife, Mickie, and their family are such wonderful people, hard workers. They did a great job raising those kids. That’s why this family is so special to me.’’

“It’s been a great friendship,’’ Fosina said. “It’s not like we latched on as friends when he became The Great Mariano. We’ve been friends since Day 1. It is a true friendship.’’

They ride to the ballpark nearly every day and you can get a glimpse of Fosina’s sense of humor from this story:

“When I pick him up for a game, I hit the horn and I wait,’’ Fosina said. “Then I move over to the passenger side and he drives my car.’’

One recent day at the Stadium, autograph seekers shouted to Joe, “How do you get Mariano to drive your car?’’

“Easy,’’ Fosina said with a smile. “I pay him $10 an hour.’’

Turning serious, Fosina said, “It’s a friendship of families, my wife, Mickie, talks to Clara all the time. They talked today. We help out with the church and other things we can do. It’s been a two-way street — he needs something, he calls me, we need something, we call him.’’

Rivera, 43, is restoring a church in New Rochelle, and Fosina is heavily involved in the community. He has been president of New Rochelle Pop Warner the last 35 years. Before that, he coached for 10 years. This time of year you can find him on Joe Fosina Field, if he is not at Yankee Stadium.

The greatness of Rivera is measured in those 693 saves (651 in the regular season and another 42 in the postseason), but it also is measured in his relationships, and there is no stronger clubhouse bond than Mo and a guy named Joe.

Joe and Mickie were Mariano’s guests for a trip to Panama in 1999. Not only did Rivera pick them up at the airport, he personally handled all their baggage. If you think Rivera is big here, Fosina explained, wait until you see him in Panama.

“At the toll booths, they would just see his car coming and the gates would go up and he’d go flying right through,’’ Fosina said with a smile.

Joe’s son Michael is an executive director at a hospital, and Rivera has quietly helped raise money for different hospital causes. When Joe’s daughter Ann Marie, who teaches autistic children, was recently honored at Yankee Stadium by the morning show “Live with Kelly and Michael’’ in a teacher of the year contest, part of the festivities included being greeted at home plate by none other than, you guessed it, Mariano Rivera.

“We were kind of laughing,’’ Fosina said of that day. “Ann Marie has known Mo forever.’’

Ann Marie’s son Timmy was born prematurely. Rivera went out of his way to befriend the child as he grew up. One day when Timmy was about 11, Joe mentioned he needed to buy Timmy a new baseball glove.

Mo casually told Joe: “Here, take this one.’’

“Mo gave me his game-used glove and said, ‘Bring this home to Timmy,’ ’’ Fosina said. “I told him, ‘No, this is your game glove.’ ”

“That’s OK,’’ Rivera said. “Timmy needs it. Now don’t lose it.’’

Timmy is 16 now and still has that glove. It sits in a protected case.

When Timmy’s friends see the glove, they ask, “How did you get that?’’

Timmy tells them, “Mariano gave it to me.’’

Joe smiled and said, “No one believes him. But only Mariano would do something like that. There are just a lot of things that makes Mariano such a good friend.’’

Fosina’s son Gary has a passion for food, as does Rivera, and the two got together in the restaurant business for Mo’s New York Grill.

Joe splits his time between the Yankees and the New Rochelle Pop Warner program, helping so many children play football, including Ravens star running back Ray Rice, who told News12 Westchester that Fosina is “a great man, a great father figure, a great leader.’’

“Mo and I have done a lot of things together and away from the field I would say Mariano is a little more relaxed,’’ Fosina said. “We’ve done some dumb things, too. He and I sat at LaGuardia Airport for an hour and a half to pick up his wife one day while she’s sitting at JFK. Another time at the airport, he went inside and I was in a no-parking zone. By the time he came out, a tow truck came and put the car on the hook and I’m up in the air, still in the car.’’

Fosina then told a story about going to see the local fireworks show that first year Mariano was with the Yankees.

“I knew the cops well and I said, ‘Listen, I’ve got Mariano Rivera of the Yankees here, can’t we put him in the roped-off area so people won’t bother him?’ ”

“No, we can’t do that, Joe,’’ he was told.

So Rivera and the two families watched the fireworks together with everyone else as Rivera pleasantly signed autographs. The next year a special roped-off area was waiting for Rivera.

He stayed on the general public side and enjoyed the night.

“Mariano just doesn’t forget the people that he has had a relationship with through the years,’’ Fosina said. “He doesn’t think that he’s up here and they are down there. His friends are really his friends.’’

Friends for life. That’s Mo and Joe.