The Kawasaki Racing rider goes into Sunday's two races leading the points standings by 37 from Aprilia Racing's Eugene Laverty.
Sykes, normally the dominant force in qualifying which he has turned into a series of race wins this season, was only seventh quickest on the opening day at Jerez with a best lap time of one minute 43.114 seconds.
Quickest was Davide Giugliano on the Althea Racing Aprilia, with fellow Italian Marco Melandri second on the BMW and Irishman Laverty in third.
Fourth fastest was Toni Elias on the Red Devils Roma Aprilia and then came Frenchman Sylvain Guintoli.
With Laverty leading team-mate Guintoli by a single point, the battle for second place in the series will probably focus most attention on Sunday.
With Sykes leading the standings by 37 points and a maximum of 50 available to Laverty and Guintoli should they win both of Sunday's races, Sykes could wrap up the title in the opening outing at Jerez.