Rick McDonald, New York Piano (Bar) Man

Chris Erikson, New York Post

Sitting amid a festive crowd in a dim Midtown bar on a recent night, working the keys of a battle-scarred upright, piano man Rick McDonald is upholding several traditions.

He’s doing his part to keep the classic American songbook alive, rolling through chestnuts such as Rick McDonald At The PianoIrving  Berlin’s “Another Cup of Coffee” and Rodgers and Hart’s “The Lady Is a Tramp.” He’s upholding a family tradition — when he was growing up in Ireland, household singalongs were a standard form of rainy-day entertainment.

And as one of the resident piano men at Bill’s Food and Drink, he’s carrying on the tradition of the legendary piano bar Bill’s Gay Nineties, which occupied this East 54th Street townhouse for 88 years.

When Bill’s was shuttered in March 2012, it was a blow to fans of the former speakeasy — and also to fans of McDonald, who played there weekly for a dozen years.

But with the space reopened last November, Bill’s piano is back in business — and so is McDonald, who was brought back in April by the new owners, restaurateur John DeLucie and his Crown Group Hospitality, who also operate Crown and the Lion.

We wanted to maintain the old New York saloon feel as much as possible,” says DeLucie — which, in part, meant keeping the piano pedals pumping nightly from 8 p.m.

So it was that McDonald, in suit and tie, took his place at the bench on a recent Wednesday and got to business doing something at which he’s become expert during 30 years of playing city barrooms — working a crowd.

He starts slow, with incidental music that won’t drown out dinner conversation. But after a while he picks up the pace, singing in a winsome tenor: “Accentuate the Positive” by Johnny Mercer, and “Luck Be a Lady” from “Guys and Dolls.”

People take up spots around the piano, and as McDonald swings into a Billy Joel medley — “The Stranger” segueing into “You’re My Home” — the vibe spreads to the bar, where a pair of middle-aged guys start belting along. “Great song,” enthuses one.

Next up is the Sinatra favorite “That’s Life,” and by the time McDonald hits “I pick myself up and get back in the raaace,” the low-ceilinged room is under his spell, fists pumping, voices lifted.

“Look at the way he gets the crowd going,” says Denise Sturm, a vice president at a securities firm, who’s gone to hear McDonald weekly for 20 years. Often this was at Bill’s Gay Nineties, and “when it closed, I was devastated,” she says. “Now it’s like finding an old friend again. He plays these old wonderful songs, and everyone comes together and sings, and it just warms your heart.”

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