Justin Timberlake's already fabulous life now appears to be overflowing with hot-and-cold-running starlets. Just days after he reportedly did some snowboarding and snuggling with Jessica Biel at the Sundance Film Festival, he was spied steaming things up with Scarlett Johansson over Super Bowl weekend in Miami.

Us reports the seemingly irresistible crooner winged into town just after midnight on Feb. 4 and wasted no time reconnecting with the stacked starlet, who guest stars in his "What Goes Around ... Comes Around" video and was seen spending quality time with him -- and his mom -- shortly after his three-plus-year romance with Cameron Diaz, 34, tanked.

Justin, 26, and Scarlett, 22, purportedly partied into the wee small hours before turning up together to watch the gridiron action in a private stadium suite.

"They were affectionate and laughing," a mole tattles to the mag.

But did the big game put Scarlett in the mood to make a forward pass? The New York Post claims her backfield was very much in motion when she and Justin hit a post-Super Bowl shindig at hot spot Mokai.

"They were talking, dancing, holding hands all night -- it was very cozy," a spy relates to the paper. "Then, as they left through the back, Justin was leaning against the wall and Scarlett came up, leaned into him and did a sexy, little dance, grinding into his body."

The "SexyBack" singer and the reigning Sexiest Woman Alive (a title previously held by Biel, by the way) then made their way to the Delano Hotel, where they hunkered down in a room for "several hours," says Us.

"Scarlett did come down to hang out with Justin, and they do like each other," an insider tells the magazine, before needlessly cautioning, "They are not serious yet."

And what of Biel, 24, whose tête-à-tête with Timberlake at a post-Golden Globes bash is said to have incited the wrath of Diaz?

A source tells In Touch that the hard-bodied starlet, who could easily take Johansson should they ever decide to duke it out for Justin's affections (a scenario he's probably played out in his head on more than one occasion) is "still in the picture," but insists, "Scarlett and Justin are totally back on."

Meanwhile, in between supposedly showing off her hip-shaking limberness last weekend, Johansson also got lucky (well, more so) when her famous name just happened to be the one picked as the winner of a one-year lease on a $1.5 million Miami Beach condo.

But don't expect the actress to lose her peaches-and-cream complexion by soaking up harmful UV rays at her new seaside pad. Turns out she's planning to hand over the swanky digs to a worthy cause.

"She won the lease, [but] we made a decision that day to donate it to a children's organization," her rep tells the New York Daily News. "Possibly Miami Children's Hospital, so visiting parents have a nice place to stay."