In the clip, which was posted to his Instagram feed, the “Bailando” singer initially gave the female fan a kiss on the cheek while posing for a selfie during a meet and greet.
However, things took a steamy turn when the fan turned her head and began passionately kissing the singer on the lips.
Rather than turning away, Iglesias, 47, continued making out with the mystery woman, at one point moving his hands toward her backside.
They continued to hold onto the peck for a few seconds before Iglesias finally let go of her and ran off with a giant smile on his face.
“Friday night in #LASVEGAS @resortsworldlv see you tonight!!!!,” he captioned the video.
Fans were divided over the intimate moment, with some expressing their jealousy and others asking about his tennis star partner.
“So lucky! You are the best to your fans! 😍,” one fan commented, with another joking, “What happens in Vegas, stays in Vegas 😂😂.”
A third commented, “Oh my God!! I want to be her,” while another stuck up for Kournikova, writing, “I don’t like it when other girls kiss you! Your kisses must only be for Anna ❤️ ❤️ ❤️.”
Iglesias and Kournikova, 41, have been dating since 2001 when they met on the set of his “Escape” music video. They briefly split in 2013 but got back together. While they aren’t legally married, Kournikova has “Iglesias” listed as her last name in her Instagram bio.
The two share three children: twins Nicholas and Lucy, 4, and Mary, 2.