Organizers said the event kicked off the first of four opening days with 1,287 players.

If the same number register over each of the four opening days, the 5,150 total would be far fewer than the 8,773 who participated last year.

Fewer entrants means the prize pool will likely be smaller. According to the payout structure sheet, this year's winner is likely to take home $7.6 million, less than the $12 million awarded to last year's winner, Jamie Gold.

It would mark the first decrease in the number of entrants at the $10,000 buy-in main event since 1992 and was widely blamed on a U.S. law signed by President Bush in October that cracks down on online gambling.

The law prohibits banks and other payment processors from handling cash transactions from U.S.-based players to and from online poker sites, which prevented many online qualifiers from lining up to play.

"Last year you had PartyPoker.com sending a ton of people. You had ParadisePoker.com sending quite a few, you had SunPoker.com and all the other smaller sites," Bluff magazine publisher Eric Morris said. "And they're not filling the seats this year."

Tournament commissioner Jeffrey Pollack said organizers were focused on making the tournament better, not necessarily bigger.

"Whether it's 4,000, 6,000, 8,000, or 10,000, this will still be the biggest, richest, most prestigious poker tournament in the world," Pollack said. "Whoever wins will walk away a multimillionaire, lives will be changed and some great poker will be played."

The tournament had set up a high-tech tent area for several tables of play outside the host site Rio hotel-casino — giving it a capacity for 12,000 players over the first four days — but abandoned it after temperatures soared above 110 degrees and it was difficult to keep cool. Players also lined up nine to a table instead of 10 last year.

But the odds against making it through the large field were still colossal.

As usual, play began in a circus-like atmosphere. Las Vegas entertainer George Wallace announced the traditional "shuffle up and deal!" Comedians Ray Romano and Brad Garrett, from the TV series "Everybody Loves Raymond," yucked it up as ESPN camera crews rolled. "Are you able to get his entire nose in the shot?" Garrett quipped.

Jeff Madsen, a 22-year-old who became the youngest player to win an event bracelet last year, then followed up with a second, appeared in a black and red jester suit after losing a bet with pros Gavin Smith and Joe Sebok. Smith was also to appear as a clown on his starting day.

"Maybe people will play different against me because they think I'm a joke," Madsen said.

And in World Series tradition, the first player got knocked out, losing their $10,000 buy-in, within the first 10 minutes of play.

Luke Staudenmaier, a 21-year-old online poker player from Pittsburgh, called an all-in raise before the flop with pocket aces. When his opponent showed an ace and king of clubs, Staudenmaier said he was "elated," because he was a huge favorite to double up his chip stack. But his opponent made a flush, and Staudenmaier's million-dollar dream ended.