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- The son of a former footballer, Portilla entered Racing de Santander's youth academy at nine, alongside cousin Carlos Mata, after allegedly receiving an offer from Deportivo de La Coruña after a tournament, which his father turned down.
After playing with the B side, he first appeared with the seniors on March 12, 2006, during a 1–2 loss at Atlético Madrid, adding two more league matches during the season. During his first years, he could only amass another match with the main side and, in January 2008, was loaned to Racing de Ferrol, as the Galicians were finally relegated from division two.
To further continue his development as a player (still aged 20), Portilla was loaned again in the following season, moving to SD Ponferradina, in the third level. For 2009–10, he was bought by Sporting de Gijón, with Santander having an option to re-acquire the player in three years. In his first year, he spent time with both the first and second teams, the latter in division three.