The Keeping Up with the Kardashians star, 31, turned up at the Encore Beach Club alongside Harden, 25.
The duo chatted throughout the day as they spent time with Kardashian's friend Malika Haqq, Jermaine Dupri and former NBA star Rick Fox.
Kardashian and Harden, who have sparked dating rumors over the past month, lounged in private cabana while temperatures that hit triple digits.
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Although neither Kardashian nor Harden were openly affectionate, she was spotted sitting on the Houston Rockets player's lap before she left around 5 p.m. Harden was seen leaving shortly afterward.
Kardashian is currently separated from estranged husband Lamar Odom. She filed for divorce from Odom in December 2013 after a very public cheating scandal and his relapse into drug abuse. The divorce has yet to be formally finalized.
The reality star was most recently linked to rapper French Montana, whom she dated on-and-off from the spring of 2014 to March 2015.