Diaz returned to defend his IFC Welterweight Championship against the man who defeated him one year earlier, Jeremy Jackson at IFC Warriors Challenge 18. This bout was for Diaz's IFC United States Welterweight Championship, Jackson's IFC Americas Welterweight Championship and the vacant ISKA-MMA Americas Welterweight Championship. Diaz won the rematch via TKO in the first round. Taking notice of his success, the UFC signed Diaz over the summer and he made his debut at UFC 44, completing the trilogy against Jackson and submitting him with an armbar in the last round of a back-and-forth fight that Diaz appeared to be winning on the scorecards.