The Dutchman struggled home 23 seconds ahead of Tony Rominger, who burst out from the chasing pack in the final kilometre in another demonstration of his phenomenal power. The late surge allowed the Swiss to add a few more seconds to the overall lead he has held for 17 successive days.
Rominger beat the third-placed Pedro Delgado to the top of the final first-category hill by 10 seconds with another Spaniard, second- placed Mikel Zarrabeitia, a further two seconds back.
Voskamp, who rides for the Dutch TVM team, was one of three riders to break away from the main bunch after only 10km. In company with Italy's Fabio Roscioli and Julio Cesar Cadena of Colombia, he was still nearly five minutes clear with most of the stiff mountain work done and only 25km left. Roscioli and Cadena fell away in the last 10km but Voskamp held his form on the descent into Oviedo and was just over three minutes ahead when he hit the first ramps of the Alto de Naranco.
He was only 1min 18sec clear as he went under the final kilometre sign, but the chasing Rominger never had him in sight.
Today's 18th stage covers a tough mountain route starting and finishing in the walled city of Avila, north-west of Madrid.Reuse content