"They partied and seemed really at ease together," a source said.
Lopez and Chmerkovskiy were spotted in the VIP area of the club, along with her entourage and one of his friends. The group apparently celebrated one of the singer's crew members' birthday.
Chmerkovskiy and Lopez met in November 2013, when they performed together at the American Music Awards. Lopez, whose break-up with dancer Casper Smart was revealed on June 6, had earlier denied that she was dating anyone.