“A lot of people say I sing old songs, but I like ’em better than the new ones,” Tony Bennett candidly told the audience at The Chelsea after reprising his signature track, “I Left My Heart in San Francisco” — during which Lady Gaga was offstage, finishing another intricate wardrobe change and/or stepping aside so the seasoned standards singer (sixty years her senior) could treat ticketholders to another solo. However, it seems that the pop singer is currently in strong agreement with her touring partner, as she humbly took on his classics with a restrained, flirtatious spin throughout their Cheek to Cheek concert, all for the sake of complementing — and never overpowering — the legend she’s recently befriended.

Read more Tony Bennett & Lady Gaga’s ‘Cheek To Cheek’ Debuts at No. 1

The two kicked off their series of 2015 performances at Las Vegas’ intimate, vintage-designed venue inside the Cosmopolitan hotel. Originally scheduled to only take the Mophie stage on New Year’s Eve — before hitting The Wiltern in February, Hollywood Bowl in May and Radio City Music Hall in June (among other dates nationwide) — their late addition to the Strip’s already-packed events calendar quickly sold out to followers of both chart-toppers. Formally suited fans and moderately-dressed “little monsters” (relative to Gaga’s other arena jaunts) sat side-by-side for a decadent 95-minute set, featuring a whopping 28 songs with a 22-person band amidst curtains of dripping jewels (similar to the hotel’s three-story bar, The Chandelier).

During their Cheek to Cheek numbers like “Anything Goes,” “Firefly” and “I Won’t Dance,” and the 2011 Duets II track that started it all, “The Lady is a Tramp,” Bennett and Gaga — a pairing she referred to as “Tony Gaga” — shared laughs, traded kisses and danced hand in hand, a genuine candor showcased in their PBS special this past October. “There’s nowhere I like to be better than cheek to cheek with Tony Bennett,” she smiled at one point. “Don’t be jealous, ladies — or gentlemen!” Bennett later quipped back, “Lady Gaga and I just did an album together — you better buy it because she really needs the money!”

Their generous set, generally celebrating Bennett and his lasting musical influence, also included welcomed solo sections, during which each remained on one side of the stage with their own band (piano, drums, guitar and double bass). Vocally, Bennett hasn’t missed a beat, effortlessly holding out songs’ closing notes for new and elaborate peaks of familiar tracks like “They All Laughed,” “Sing, You Sinners” and “The Best Is Yet to Come,” among many, many others. He spontaneously cracked a joke about front-row attendees who arrived late, and before singing “Smile,” he said he received a note during its chart reign that read, “‘Tony, thank you for resurrecting my song,’ and the letter was signed, Charlie Chaplin.”

See more Watch Lady Gaga, Tony Bennett Get Festive for the Holidays

Gaga, free of a pop show’s heavy production — visually and musically, as she said, “It’s a wonderful break for me to play with real musicians” — shined bright when theatrically relishing in the quiet moments of songs like “Lush Life,” “Bewitched, Bothered and Bewildered” and “Ev’ry Time We Say Goodbye” (the latter dedicated to her “mother, father, and my darling Taylor [Kinney]” in the audience), or personably cha-cha dancing across the stage during “Bang Bang (My Baby Shot Me Down),” switching “my baby” to “that asshole” at one point and even flicking off the song’s said man, to much applause. She remained authentically reverent throughout the set, well aware of her spot in Bennett’s long-standing legacy and never aiming to seize the spotlight (except with seven shimmering outfits of feathers, ruffles and tassels). Often, she shared comments of disbelief: “Do you know that this man is the oldest living legend in the world? But he’s the youngest guy I know.”

Before the show’s confetti-filled closing, Gaga noted a thought she has when alone in her hotel room. “I dream of Tony Bennett and how he’s opened my mind with his wisdom, decades of music,” she said. “Life is all about how you keep going, right? With your passion. … It will keep you happy forever.” The sentiment was not only fitting for an audience contemplating the year ahead, but also for a pair who, very visibly and harmoniously, seem to find the happiness they seek, when they’re out together dancing, cheek to cheek.

Set list:

Anything Goes
Cheek to Cheek
They All Laughed
The Good Life
The Lady’s In Love With You
Nature Boy
How Do You Keep the Music Playing
Sing, You Sinners
Bang Bang (My Baby Shot Me Down)
Bewitched, Bothered and Bewildered
Firefly
Smile
When You’re Smiling
Steppin’ Out With My Baby
I Won’t Dance
For Once in My Life
The Best Is Yet to Come
I Can’t Give You Anything But Love
Lush Life
Sophisticated Lady
Watch What Happens
Let’s Face the Music and Dance
Ev’ry Time We Say Goodbye
I Left My Heart in San Francisco
Who Cares (So Long As You Care for Me)
But Beautiful
The Lady Is a Tramp
It Don’t Mean a Thing (If It Ain’t Got That Swing)

Email: Ashley.Lee@THR.com
Twitter: @cashleelee