While a sea of ad buyers were snacking and boozing over at Fox’s annual party at Wollman Rink in Central Park, a smaller group of Upfront guests headed a bit further downtown Monday evening to dance with Jennifer Lopez at a private concert, put on by Telemundo.

The Hammerstein Ballroom was swarming with ad-types young and old who were fascinated by Lopez’s high-energy stage presence, multiple costume changes and close proximity. The intimate venue welcomed about 1,200 concert-goers, a fraction of the packed houses J.Lo usually attracts on world tours or her current Las Vegas residency.

Kicking off the concert with her 1999 hit “If You Had My Love,” Lopez came out in a black leotard, adorned with metallic overlay and thigh-high boots. Warming up the crowd who’d been up and down town all day, she yelled, “Telemundoooo! Is work over?” to which the audience cheered, as they sipped on cocktails and dined on food of Latin, Asian and American cuisine.

The J.Lo concert came hours after Monday morning’s NBCUniversal mega Upfront, which for the first time, consolidated all of the NBC properties, including Telemundo. Lopez was on hand at the Radio City Music Hall presentation to represent her NBC cop drama “Shades of Blue,” which is renewed for a second season. This past TV season, Lopez was a staple on both NBC and Fox, as a judge on the final season of “American Idol.”

Using the superstar to headline Telemundo’s party — a shot at Fox — is the latest effort in wooing ad buyers this Upfront season, which is expected to bring in 5% to 9% more advertising dollars this year, around $9 billion. Since 2009, both company’s parties have ran head-to-head, but bringing on Lopez upped the ante.

Singing everything from “Jenny From the Block” to “Waiting for Tonight” to “Let’s Get Loud” — which ended by blasting confetti — and a beautiful Spanish ballad, Lopez closed the concert with her latest single “Ain’t Your Mama.”