The 2011 season saw Diaz join Level 5 Motorsports for its P2 program. He kicked off the season with a class win in the 2011 12 Hours of Sebring with Scott Tucker and Ryan Hunter-Reay before earning additional victories at Road America and Laguna Seca. Diaz remained at Level 5 Motorsports for 2012, earning the P2 victory at Laguna Seca in the team's HPD ARX-03b.