Lady Gaga and Tony Bennett performed Friday and Saturday at the Kennedy Center. (Daniel Swartz/Courtesy of Kennedy Center)

Now that Lady Gaga has proved that she can knock out a jazz standard like an old Broadway pro, it didn’t come as a shock when the pop star did just that — repeatedly — alongside singer Tony Bennett on Friday night.

But her pasties? Those were a surprise.

Unlikely as their collaboration may seem, Gaga and Bennett don’t flout much tradition on their charismatic, respectful collection of duets, “Cheek to Cheek.”

Nor did they flout tradition during the first of two performances at the Kennedy Center over the weekend. That might explain the murmuring from the audience when Gaga — in one of many costume changes — strode onto the stage sporting an Elmo-red get-up and two strategically placed, er, chest accessories.

Bennett just smiled in that winking, Bennetty way, and the show soft-shoed on.

With his 89th birthday arriving Monday, Bennett doesn’t need anyone’s help to stay beloved; he’s managed fine on his own by just being an American treasure. Each time he wings through the capital, he scoops up another award — last week’s catch was a President’s Medal from George Washington University — and his name is probably on something shiny at the Kennedy Center, which made him an honoree in 2005.

Gaga, his 29-year-old student, is at a different stage in her career: She lorded over pop music from 2008 to 2012, but her 2013 record “Artpop” sold modestly compared with her earlier smash “Born This Way.”

With Bennett, she’s found both a fresh start and a challenge.

It’s less clear what Bennett is getting out of the deal. Then again, there are less entertaining ways to live out one’s silver-haired years. So if the 17-time Grammy winner is just in this for the thrill, well, party on, dude.

For an hour and a half Friday — with a few breaks backstage — the Queens native peeled off classics like bills from a gilded money clip, cozy both on his own and with his duet partner locked to his shoulder. Content to stand center stage or adjacent to a piano, he didn’t do any back flips, but his trusty corn husk of a croon took care of the maneuvering. He even trotted out his party trick of singing “Fly Me to the Moon” unamplified, just to show the guy’s still got it. As if there were a doubt.

Gaga glammed it up and hammed it up, clearly delighting in playing the equivalent of a teen who arrives at a Christmas dinner with a fresh tattoo. But after cresting Mount “Lush Life” and a crisply enunciated “La Vie en Rose,” the singer born Stefani Germanotta earned each standing ovation she got.

Bennett doesn’t have many new tricks up his sleeve; his joke about wanting to sell copies of “Cheek to Cheek” because Gaga “really needs the money” is one he’s cracked before. But when you have Gaga acolytes in the crowd screaming the S-word — “Yes, Gaga, [expletive]!” one cried — there’s no need for pyrotechnics. The pasties, though — those didn’t hurt.

Schweitzer is a freelance writer.