Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L) and challenger Bulgarian heavyweight boxer Kubrat Pulev exchange punches during their title fight in Hamburg, November 15, 2014. World heavyweight champion Vladimir Klitschko knocked out Bulgarian challenger Kubrat Pulev with a fierce left hook in the fifth round on Saturday to retain his IBF title and end his opponent's unbeaten record. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) lands a punch during his title fight against challenger Bulgarian heavyweight boxer Kubrat Pulev in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L) delivers a punch to his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) and his challenger Bulgarian Kubrat Pulev exchange punches during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) and his challenger Bulgarian Kubrat Pulev exchange punches during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Photographers take pictures as challenger Bulgarian Kubrat Pulev and Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) exchange punches during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) knocks down his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Challenger Bulgarian Kubrat Pulev jokes with the referee after being knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (not pictured) during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) lands a punch during his title fight against challenger Bulgarian heavyweight boxer Kubrat Pulev in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (R) lands a punch during his title fight against challenger Bulgarian heavyweight boxer Kubrat Pulev in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko knocks down his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Photographers take pictures as challenger Bulgarian Kubrat Pulev is knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (not pictured) during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko knocks down his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko knocks down his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko knocks down his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Challenger Bulgarian heavyweight boxer Kubrat Pulev (R) lies in the ring after being knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L), who celebrates with his brother Vitali (2nd L), as referee Tony Weeks checks on him after their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Challenger Bulgarian heavyweight boxer Kubrat Pulev lies in the ring after being knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Challenger Bulgarian heavyweight boxer Kubrat Pulev (R) lies in the ring after being knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L), who celebrates with his brother Vitali (2nd L), as referee Tony Weeks checks on him after their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Challenger Bulgarian heavyweight boxer Kubrat Pulev lies in the ring after being knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (not pictured) during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Referee Tony Weeks checks on challenger Bulgarian heavyweight boxer Kubrat Pulev (R) who was knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (L) after their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko reacts after defeating his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko cheers with his supporters after defeating his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko reacts after defeating his challenger Bulgarian Kubrat Pulev during their title fight in Hamburg, November 15, 2014. (Photo by Morris Mac Matzen/Reuters)

Challenger Bulgarian heavyweight boxer Kubrat Pulev applies an ice pack to his face after being knocked down by Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko (not pictured) after their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)

Ukrainian WBA, WBO, IBO and IBF heavyweight boxing world champion Vladimir Klitschko celebrates with a Ukrainian flag after he knocked down challenger Bulgarian heavyweight boxer Kubrat Pulev (not pictured) during their title fight in Hamburg, November 15, 2014. (Photo by Fabian Bimmer/Reuters)