Wearing a black crop top paired with pants and sneakers, Lopez was "having a really great time" dancing to the sounds of DJ Mike Attack, a spy told Page Six.
The audience was surprised when Mars sang along from the DJ booth to his own hit songs "Locked Out Of Heaven" and "Bubble Butt."
While "Locked Out Of Heaven" is the lead single from Mars' second studio album titled "Unorthodox Jukebox" released in 2012, "Bubble Butt" is the fourth single of Major Lazer's second studio album titled "Free The Universe" featuring Mars along with Tyga and Mystic.
With other friends and her manager, Benny Medina, Lopez attended Mars' concert in Las Vegas and after party at hotspot Marquee in the Cosmopolitan.
In his extended run, Mars performed at Chelsea before the party.
Also spotted in the VIP area at the party was Academy Award winner Matt Damon with a group of friends and the group of Lopez, who will return as a judge in the upcoming 14th season of "American idol" with Keith Urban and Harry Connick, Jr.
Meanwhile, the current head coach for the University of Kentucky Wildcats women's basketball team known as UK Hoops, Matthew Mitchell recently impersonated Mars at Rupp Arena performing a rendition of one of his hit songs.
Dressed up as Mars, Mitchell sang "Just The Way You Are" with lyrics changed to suit Big Blue Nation as a part of his musical tribute with an over-the-top dance entrance, which he traditional does at the Wildcats' annual Big Blue Madness facilities, Heavy reported.
The event was also attended by Drake, who was dressed in UK warmups. The 27-year-old rapper and jumped into the layup line of the Wildcats.
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