Portas stayed with Ferrero to 3-3 in the opening set before the top seed broke for the first time and consolidated with a love service game for 5-3.
Ferrero, born just outside Valencia and cheered on by a crowd of around 3,000, went on to take the set and broke in the third game of the second.
The world number three had little difficulty holding serve for the remainder of the set to clinch victory.
Ferrero will face a quarter-final clash with Agustin Calleri, the fifth-seeded Argentine who beat Dominic Hrbaty of Slovakia 6-1, 5-7, 6-2.
Calleri was joined in the last eight by his countryman Gaston Gaudio, who completed a comeback victory over Spain's Galo Blanco after their match had been called off on Wednesday night due to bad light.
Gaudio, who won the title last year when the event was played in Mallorca, resumed on Thursday with the match level at a set apiece.
The number four seed broke in the final game of the decider to clinch a 3-6, 6-4, 6-4 victory and a quarter-final against Flavio Saretta of Brazil.
The surprise presence in the quarter-finals is the Armenian Sargis Sargsian, who beat Franco Squillari, another Argentine claycourt specialist 7-5, 3-6, 6-3.
He will take on Christophe Rochus after the Belgian beat Markus Hipfl of Austria 6-4, 6-0.
