Izumi made his mixed martial arts debut against New Zealand kickboxing specialist, Antz Nansen for Japan's Sengoku promotion in September 2009 after Izumi signed with World Victory Road. Instead of using his judo techniques to his advantage during his debut, Izumi attempted to trade punches with the world-class striker. Izumi was beaten badly in his debut and lost the fight by TKO.
After his poor performance in his debut, Izumi began turning his mixed martial arts career around. At Dynamite!! 2009, representing Sengoku, he won via unanimous decision over Katsuyori Shibata. After being dominated through the first few rounds, Izumi came back in the second half of the very final round, landing a great sequence of punches and controlling Shibata on the ground, where he utilized many hammerfists. This win was very significant because Izumi's father was vocal in saying that if Izumi was defeated again, that he would take his son out of MMA and return to judo.