He set a decathlon personal best of 8057 in his home town of Havana in March 2008, breaking the 8000-point barrier for the first time. Díaz's first appearance on the global stage came soon after at 2008 Summer Olympics, but he did not compete in his specialist event but rather as part of Cuba's 4×400 metres relay team with Yunier Pérez, William Collazo and Omar Cisneros. The team failed to progress beyond the heats stage of the competition. He won his first senior medal the following year in Havana at the 2009 Central American and Caribbean Championships in Athletics, finishing as runner-up behind compatriot Leonel Suárez but managing to score over 8000 points for the second time in his career with a final total of 8013.