The Olympics’ most decorated champion, MICHAEL PHELPS, is still drinking like a fish even though he’s been charged with a DUI!

As these exclusive EN­QUIRER photos show, the 27-year-old champ was having such a good time partying at a recent Las Ve­gas blow-out, he nearly lost his pants!

“Michael is a party ani­mal!” a fellow reveler told The ENQUIRER.

“He appeared to be drunk and his pants nearly fell off right in the middle of a crowded bar!”

And with Michael ’ s GF Megan Ros­see nowhere in sight, the source added that Phelps “was flirting with every pret­ty girl in sight.”

The swimming superstar, who was charged with a DUI in 2004, was boozing like a mad man on Oct. 22 at XS Nightclub at Encore in Las Vegas. In return for Phelps’ 2004 guilty plea to driving while impaired, prosecutors agreed to drop charges of driving under the influence, underage drink­ing and failure to stop at a stop sign.

“Michael was constantly surrounded by beautiful women,” said the source. “He was having a ball.

“At one point he decided to crowd surf inside an in­flatable raft at the club. But he barely made it a few feet before he completely fell over on his behind. He was so into it he wasn’t even em­barrassed. Thank God he didn’t get hurt.”

The source said the record 22-time Olympic medal winner – who made headlines three years ago when a photograph of him smoking pot appeared in newspapers around the world – “had very red eyes and looked and acted like he was feeling no pain at all” dur­ing his Vegas romp.

Sadly, while the swim­ming ace was partying up a storm with some seriously sexy ladies, his clueless girlfriend was thousands of miles away. Blonde model Megan tweeted a photo of a large plate of food she was about to eat, apparently completely oblivious to her man’s Sin City activities.

Added the source: “Michael was definitely acting single and ready to mingle!”