Like several other fighters in the promotion, Rothwell was competing for the coach who he trained with regularly. On April 29, 2006 Rothwell made his IFL debut against future UFC veteran, the Polish-Canadian fighter, Krzysztof Soszynski. In the first round, Soszynski surprisingly decided to exchange strikes with Rothwell, and landed a left uppercut and held his own until he was knocked down by a short left hook from Rothwell, who then slammed Soszynski to the canvas. After working from side control and then standing again, Rothwell landed a series of punches at the end of the round, that knocked down Soszynski, and then followed this up with more punches to his downed opponent. Despite the round ending, referee Dan Miragliotta called a stop to the contest, granting Rothwell the win via TKO. After racking up four consecutive IFL wins, he fought future "" winner and IFL Heavyweight Champion Roy Nelson, winning via split decision. His next fight was a rematch from almost five years earlier against veteran Travis Fulton, owner of 195 career victories. Three minutes into the second round, Rothwell secured a kimura, causing Fulton to submit. Rothwell then met Krzysztof Soszynski in a rematch of his IFL debut. Rothwell once again won via TKO, only 13 seconds into the bout. His last fight in the IFL came against former UFC Heavyweight Champion, Ricco Rodriguez in the team finals. After controlling the fight and displaying superior striking, Rothwell won the fight via unanimous decision. However, the Silverbacks fell short of a victory and lost the championship to Renzo Gracie's New York Pitbulls. This was Rothwell's last appearance in the IFL, as he eventually left the organization due to a contract dispute. During his time in the IFL, Rothwell had a 9–0 record. After leaving the IFL, Rothwell joined Affliction where he appeared in only one bout, against former UFC Heavyweight Champion Andrei Arlovski, Rothwell lost the fight via knockout due to an uppercut in the final round. This ended Rothwell's 13-fight win streak and gave him his first defeat in over three years. Rothwell made his UFC debut on October 24, 2009, at UFC 104 against undefeated Cain Velasquez losing via TKO one minute into round two. The stoppage was controversial, because Rothwell seemed to be getting to his feet as Steve Mazzagatti stopped the fight.