[2] After transitioning to Seidokaikan in 1993, Thompson fought his first match against Taiei Kin at the K-1 Grand Prix '93 in Tokyo, Japan on 30 April 1993, losing by majority decision after two extension rounds were needed to separate the pair.
Entering the 1993 Seidokaikan Karate World Cup on 3 October 1993, Thompson rematched Kakuda in the tournament's opening stage and repeated his performance to score another first-round KO.
Returning at K-1 Revenge in Yokohama, Japan on 18 September 1994, Thompson knocked out Muay Thai exponent Changpuek Kiatsongrit with a lighting-quick spinning back kick just two seconds into the third round.
Following wins over Wataru Uchida, Eiji Matsumoto and Kenneth Felter, respectively, he was stopped with a body kick from Sam Greco inside the first round of the tournament championship match.
In another tough matchup, Thompson was dropped by Ernesto Hoost a total of four times over two rounds, forcing the referee to call a stoppage at K-1 Revenge II in Yokohama on 3 September 1995.
He was unable to stay out of the losing column for long, however, as he was TKO'd inside the first round by Duane van der Merwe at the K-1 Grand Prix '96 Opening Battle in Yokohama on 10 March 1996.