Movistar, who set out last of the 22 teams, clocked a time of 14 minutes 13 seconds to pip second-placed Cannondale by six seconds in the south west city of Jerez de la Frontera.
The battle was expected to be between in-form Nairo Quintana and Alejandro Valverde but instead it was team mate Castroviejo who came through.
"We didn't want to take many risks and it worked out this way," Castroviejo told reporters.
Chris Froome's Team Sky were 27 seconds off the pace in 11th position.
There was also disappointment for the strong Omega Pharma-Quick Step team that includes Rigoberto Uran and Tony Martin. They were down in fifth spot, 11 seconds adrift of Movistar.
The time trial, featuring two hairpins and several sharp corners, is one of three stages against the clock.
The last one comes on the final day of the three-week Vuelta, with the riders finishing in front of the cathedral of Santiago de Compostela in north west Spain.
Alberto Contador wore heavy strapping on his leg but completed the time trial without any alarms as his Tinkoff-Saxo team finished seventh, 19 seconds off the lead.
Spaniard Contador, Colombian Quintana and Briton Froome are the favourites to win the Vuelta.
"I am happy, the team is very strong and I felt well supported today," said Contador. "I was pushing myself but I still need to find my rhythm."
(Editing by Tony Jimenez)
Share
