The Spanish driver clocked a best lap of two minutes 13.434 seconds in his Seat Leon to finish fastest ahead of Gabriele Tarquini in the Lukoil Racing Team Seat (2:13.632).
Another driver in a Seat Leon, Tiago Monteiro, set the early pace until his car cut out in the middle of the track forcing the session to be red flagged and restarted.
James Nash in the Team AON Ford Focus was third fastest with a 2:13.863.
Rob Huff was the fastest of the Chevrolets with a 2:14.254 to be fourth quickest, followed by Alain Menu (2:14.671).
The session gave the WTCC drivers the first chance to experience the Slovakia Ring circuit at speed and several fell foul of its tight infield corners.
The fast left-hander at turn nine is already proving to be one of the trickiest sections of the 5.913km circuit, with Stefano D’Aste, Darryl O’Young, Alberto Cerqui and Mehdi Bennani all taking to the grass at some point.