Diaz faced Strikeforce newcomer and then-DREAM Welterweight Champion Marius Žaromskis to crown the first Strikeforce Welterweight Champion on January 30, 2010 at . Žaromskis came out aggressively and the two men exchanged on the feet until Diaz tied his opponent up in the clinch and landed numerous knees to Žaromskis' right leg. Diaz then scored a takedown and looked for a guillotine choke – quickly shrugged off by his opponent. The two men continued to exchange, with Diaz utilizing his unorthodox boxing skills, until rocked by a Žaromskis left hook and falling to his back. Žaromskis landed few effective shots while Diaz was "turtled" on the floor, allowing him to recover and stand back up. In the few remaining minutes, Diaz opened up with his boxing range, tagging Žaromskis cleanly several times with combos composed of jabs, hooks and seamless bodyshots; forcing him against the side of the cage where he landed a solid uppercut that dropped his opponent leading to the referee to stop the contest at 4:38 of the first round. Diaz was then crowned the inaugural Strikeforce Welterweight Champion.