New York Mayor Michael Bloomberg's daughter has won the 50-thousand-dollar Knock-out event at a Las Vegas horse-riding contest. Twenty-two-year-old Georgina Bloomberg defeated Michael Whitaker of Great Britain in the finals at the inaugural Las Vegas World Invitational yesterday. She had no faults while riding a ten-year-old Dutch warmblood mare named Nadia. She says she was very pleased with the round and called Nadia a great speed horse.