BY MELISSA RUGGIERI

By now, most fans of Tony Bennett and Lady Gaga are beyond giving quizzical looks upon hearing that the premier jazz-pop crooner of our time and the Top 40 mainstay with a penchant for meat dresses are a musical item.

They proved last fall with the release of the duets album “Cheek to Cheek” that age and snap judgments are meaningless when genuine talent is involved.

At a steamy, sweaty, sold-out Chastain Park Amphitheatre Wednesday, Bennett – handsome devil that he is – and his respectful protégé schooled the crowd with 90 minutes of standards and verified that what might look ridiculous on paper in fact works beautifully in reality.

Flanked by a nine-piece band, including double drummers and pianists and a pair of brass players, Bennett and Gaga opened the show by bopping through jazz-inflected versions of “Anything Goes” and “Cheek To Cheek.”

The always-old-school-dapper Bennett – who, unbelievably, turns 89 next week – seemed invigorated by Gaga’s playfulness. She, meanwhile, clearly relishes the jolt of authenticity this pairing gives her career. Then again, anyone who has paid enough attention to her to look beyond the façade knows her capabilities as a vocalist.

For the majority of the set, the twosome shared the stage, trading lyrics and the occasionally awkward pose (Bennett’s hand intimately pressed against Gaga’s waist during “Nature Boy” sparked a bit of an icky feeling); but theirs is obviously a platonic affection.

During solo turns, Bennett offered “Sing You Sinners” to the happily clapping audience and effortlessly talk-sung his way through “The Good Life.” While he got off to a bit of a rough start vocally, his warm, raspy voice held the long notes in “Watch What Happens” and a robust, deeply felt version of “For Once in My Life,” which he prefaced by calling out Freddy Cole (Nat’s brother) in the crowd.

A highlight for Mr. “I Left My Heart in San Francisco” was his sparse, tender take on Charlie Chaplin’s “Smile,” a song that was perfectly complemented by Bennett’s emotive vocals.

Gaga, meanwhile, paired every entrance onstage with a glittery new outfit, including a navy pantsuit for her simmering version of Cher’s “Bang Bang (My Baby Shot Me Down”), which the band infused with Latin rhythm, and a coy “Bewitched, Bothered and Bewildered,” which featured her shuffle-sliding across the stage like Bette Midler during one her brassy numbers.

But considering how much Gaga, 29, wants to be taken as seriously as she deserves, some of her high-slit, bosom-revealing outfits – notably the red mesh-like material under a red-feathered coat that she donned for “I Can’t Give You Anything But Love, Baby” – distracted from the very point she was trying to make.

Listening to her voice swoop low, then dance across the scale during a stunning cover of Billy Strayhorn's "Lush Life" ( check out the spine-tingling version she performed on "The Howard Stern Show" last year ), would have satisfied any naysayer. She's a tremendous singer, as she demonstrated again a few songs later (in a pink ruffled number) on Edith Piaf's "La Vie En Rose." Enough with the needless flash.

But considering the amount of synthetic music cluttering the airwaves these days – and Gaga isn’t exempt – it’s both amusing and amazing that two generations of performers and fans can be united by the music of Frank Sinatra and Duke Ellington and Richard Rodgers.

A glance around the Chastain crowd found plenty of glitter-Spackled Gaga boys co-mingling with Bennett’s khaki shorts and polo shirts demo, testament to the fact that with timeless music, neither age nor gender nor personal style can interfere.

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