The highlight of his 2010 season was a fifth-place finish in the 10,000 m at the European Championships. Castillejo made his debut over the marathon distance in 2011 at the national championship race held at the Maratón Ciudad de Castellón. He won the race with a time of 2:10:02 hours – a performance which guaranteed him selection for the 2012 Summer Olympics. He defeated Patrick Makau (the marathon world record holder) at the 2012 Granollers Half Marathon in February, where he performed well in near-freezing conditions. At the 2012 Summer Olympics, he finished in 24th place.