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The bout will headline UFC 147 at Joao Havelange Stadium, a soccer venue that is expected to accommodate the largest crowd ever for a UFC event.
A record crowd of 55,724 filled Rogers Centre in Toronto on April 30 to witness welterweight champion Georges St. Pierre retain his title against former Strikeforce champ Jake Shields at UFC 129.
"This will be the biggest sporting event of the year," UFC president Dana White said on the promotion's website. "Bigger than the NFL, the NBA, you name it -- UFC 147 will be the biggest.
"The whole world wants to see this fight between Silva and Sonnen. We (will) broadcast in over 150 countries in 22 languages in half a billion homes. Wherever those fans are, they are going to be watching this fight."
The 36-year-old Silva (31-4) defends his title against Sonnen for the second time. The two met Aug. 7, 2010, at UFC 117 in Oakland, Calif.
After being dominated throughout much of the fight, Silva retained his belt by submitting Sonnen at 3:10 of the fifth and final round.
In his most recent fight, Silva registered a second-round TKO of Yushin Okami. That bout took place Aug. 27 at UFC 134 in Rio de Janeiro.
Sonnen (27-11-1) earned his second title shot with a unanimous decision over Michael Bisping on Jan. 28 in Chicago.
He has won five of his past six fights, the lone setback coming against Silva.
Middleweight contender Vitor Belfort (21-9) gets a chance to make it 2-0 against former Pride 205-pound champion Wanderlei Silva on the card.Belfort, a former UFC light heavyweight champion, defeated Silva by first-round TKO on Oct. 16, 1998, at UFC Brazil. It was Belfort's debut at light heavyweight.p> He previously competed at heavyweight.
Silva (34-11-1, with one no contest) defeated former Strikeforce middleweight champion Cung Le by second-round TKO in November at UFC 139.
The win improved Silva's record to 2-1 at 185 pounds.
Before stepping into the Octagon for their rematch, Belfort and Silva will square off as coaches on "The Ultimate Fighter: Brazil."