In a match he was considered a clear underdog, Wielzen shocked the Muay Thai world by knocking out the 'Iron Hands of Siam' via a vicious head kick after just 30 seconds.
Contender title against Imed Boukouayel - Wielzen would become involved with the It's Showtime organization, making his debut in Milan and defeating local fighter Matteo Lippi by knockout.
[8] In March 2011, Wielzen defended his It's Showtime world title once again but was unable to retain his crown, losing by majority decision after five rounds to Karim Bennoui at the event in Brussels.
[15][16][17][18] Wielzen rematched Masahiro Yamamoto at RISE 94 in Tokyo, Japan on July 20, 2013, and fell victim to a second round high kick from the Japanese fighter.
[19][20] Wielzen competed at the -65 kg/143 lb Thai Max tournament in Meyreul, France on October 19, 2013, defeating Mickael Peynaud by first-round KO in the quarter-finals before losing to Houcine Bennoui by unanimous decision in the semis.