In 2004, Harrah's Entertainment purchased Binion's Horseshoe, kept the rights to the Horseshoe and World Series of Poker brands, sold the hotel and casino to MTR Gaming Group, and announced that the 2005 Series events would be held at the Harrah's-owned Rio Hotel and Casino, located just off the Las Vegas Strip. The final two days of the main event in 2005 were held downtown at what is now the MTR operated "Binion's" in celebration of the centennial of the founding of Las Vegas. It also added a made-for-television $2 million "freeroll" invitational "Tournament of Champions" (TOC) event first won by Annie Duke as a "winner-take-all" event.

Starting in 2005, the WSOP began a tournament "circuit" at Harrah's-owned properties in the United States where in addition to the $10,000 buy-in tournament at each site, qualifying players became eligible for a revamped Tournament of Champions. The 2005 TOC, made up of the top twenty qualifying players at each circuit event, along with the final table from the 2005 Main Event and the winners of nine or more bracelets (Hellmuth, Chan and Doyle Brunson) would participate in the revamped TOC at Caesar's Palace. Mike "The Mouth" Matusow won the first prize of $1 million (US), and all the players at the final table were guaranteed a minimum of $25,000 for the eighth and ninth place finishers. During a break in the final table of the 2005 Main Event on July 16, Harrah's announced that eleven properties — including the recently added Bally's and Caesar's properties — would host 2005-06 WSOP Circuit events that started on August 11 in Tunica, Mississippi. One event that was scheduled for Biloxi, Mississippi was cancelled after the Grand Casino Biloxi, which was scheduled to host the event, suffered major damage from Hurricane Katrina.