Markina-Xemein, Spain - Alberto Contador protected his lead of the Tour of Basque Country before the decisive time trial, while Ben Swift of England won Friday's fifth stage.
Swift edged a pack of riders at the finish line to claim the 160-kilometer (99-mile) leg featuring five categorized mountain climbs from Eibar to Markina-Xemein in just under four hours.
Alejandro Valverde, who is second overall, also finished second in the stage, a wheel-length behind Swift.
Contador finished in the leading group to make sure he didn't lose any of his 12-second lead.
The 54th edition of the six-day race in northern Spain concludes on Saturday with a 24-kilometer (14.9 mile) time trial to and from Beasain.