In March 2012, Nieves was training up to four hours a day at the Galician Sports Modernization Center (CGTD). He finished first in the 2012 San Silvestre Candelaria 4,500 meter race. He competed at the 2012 Spanish national Paralympic athletic championships where he came in first in the 5,000 meters. A few months before the London Paralympics, he had problems with his tendons. He did not compete in the 2012 European Championships because of his tendon injury. As a 28 year old, he raced at the 2012 Summer Paralympics, finishing fourth in the 5,000 meters. His time was 4 seconds slower than his personal best.