How did Ashton Kutcher ring in his sixth wedding anniversary with Demi Moore on Sept. 24?
With a raucous, Demi-free party at the San Diego Hard Rock Hotel -- which, a source tells the new Us Weekly, culminated in a sexual encounter in a hot tub with local blonde Sara Leal (pictured here) and her pal in his $2,500-a-night hotel suite. (Moore, 48, was elsewhere in the U.S. promoting her directorial work for the Lifetime short film project 5.)
Prior to that early morning hot tub session, Kutcher began his night drinking vodka tonics and prowling for women with pals Danny and Chris Masterson at Fluxx nightclub -- where the pickings weren't to his liking. "He said none of the girls were 'hot-tub worthy,'" a Fluxx onlooker tells the new issue.
But Kutcher liked what he saw when he met party girl Leal and her friend past 4 a.m. in his 1,200-square-foot suite back at the Hard Rock. "Ashton told them he was separated from Demi," one source says.
After some "hard-core" flirting, the Two and a Half Men star was "totally into it," another source says. "Within five minutes, they were all naked in the hot tub, making out!"
Reps for both Kutcher and Leal didn't respond to repeated requests for comment.
Moore, meanwhile, is "struggling. She's been alone a lot lately," another pal says.
For more on Kutcher's wild night, whether he's really strayed before, why Moore still may not be ready to let go and the scoop on Leal -- pick up the new Us Weekly, on stands Friday.