Full House hunk JOHN STAMOS extortion trial begins in Michigan with shocking allegations.

Scott Sippola
, 30, and Allison Coss, 23, were busted in December 2009 after threatening to reveal publicly several embarrassing pix of Stamos allegedly with strippers and drugs.

The stand accused of trying to extort $700,000 from the former ER-star.

Defense attorneys  claim that Stamos had a fling with Coss when she was underage and have suggested they will reveal Stamos’ sex life public in an attempt to exonerate their clients.

Attorney Sarah Henderson, told the court in her opening statement that Coss had an intimate, sexual encounter with Stamos when they met in 2004, shortly after he separated from his wife Rebecca Romijn.

While the judge had ruled that testimony about Stamos’ sex life was off-limits during the actual proceedings, opening statements were fair game.

The defense attorney stated Stamos invited Coss and another girl back to his hotel suite after eyeballing the pair in a nightclub. They accompanied Stamos back to his room where two strippers soon arrived with cocaine.

Coss and her gal pal snapped pix of Stamos bending over a table laden with cocaine, Henderson said in opening statements.

Later that night, the attorney alleged, her client and Stamos had a steamy make out session, took a dip in the hot tub together with an offer of oral sex proffered by Stamos but declined by Coss, the attorney said.

Working with authorities, Stamos representative, set up a sting when they set up a cash trade for the alleged damning photos.

The attorney said her clients were attempting a legitimate business transaction.

“This is really just a get-rich-quick scheme that is based on lies and betrayal,” prosecuting attorney Maarten Vermaat said.

His attorney, William Sobel, told media: “The allegations made today in the courtroom by the defendants’ attorneys during opening statements will not be proven because they are simply untrue.”

John Stamos testified on Tuesday that he met Coss after he was taken to Florida by friends trying to cheer him up after separating from his ex, Rebecca Romijn.

“I was very heartbroken at the time,” Stamos said. He claims Coss told him she was on “college” spring break and that when they went back to his hotel room they were “just hanging out” and “socializing.”

Stamos denied things got romantic but said he later began communicating with Coss via e-mail and described their conversations as “flirty.”

Still, he said, “It was all very sweet. I considered her a friend.”

updated: 130 PM EDT first posted: 10 AM EDT