The championship, staged at Binion's Horseshoe Casino, is the biggest of the year for professional gamblers. The first prize of $1m (pounds 630,000) attracts poker players from all over the world, with British and Irish punters well represented.
In Damon's latest movie, Rounders, which is to be released later in the year, he plays a poker-playing law student who wants to give up gambling, but has to go on playing to help a friend in trouble. He showed that he could hold up the role in real life as well, looking suitably inscrutable as crowds pressing close to the tables watched his every move. His most hysterical teenage fans had to strain their eyes in longing from beyond the doors, though, because they were too young to be permitted to join the action in the gaming saloon itself.
Through all this overheated attention, young Matt displayed an impeccably cool and friendly manner. As it happened, I was seated next to him in the press tournament, to which he gained entry by virtue of being a scriptwriter. Between signing autographs and facing the cameras, he showed he could bet and raise as well as any of the press corps. But not, it turned out, quite as well as the professionals.
The star survived five hours in the world championship (entry fee $10,000) but was unlucky to be placed at the same table as two-time world champion Doyle Brunson.
Around 6pm, Damon looked down at his "hole" cards and found a pair of kings, the second-best hand you can be dealt in the type of poker played in the championship, no-limit Texas Hold 'Em. Unfortunately, Brunson had caught the one-better starting hand, a pair of aces. Fade out the teeny- boppers' dream.
So does Damon think poker is more difficult than acting? "Acting is more difficult," he reflected, before adding diplomatically, "but acting is like poker, because people think they are both very easy things to do."
After four days' play, the new world champion turned out to be a former refugee from South Vietnam, "Scotty" Nguyen, aged 35. He now lives as a professional poker player in southern California. His reward for outplaying 349 rivals in the championship was $1m cash, set out on the table in front of him. "Thank you all, this is the sweetest moment of my life, baby!" he cried.