Answer
Andy Ristie ended Giorgio Petrosyan's undefeated streak in 2007. They fought in a kickboxing match that was held in Japan. Ristie won by knockout in the second round. This was a major upset, as Petrosyan was considered to be one of the best kickboxers in the world at the time. Ristie's win was a major turning point in his career, and he went on to become a world champion.