Tejay van Garderen added vital seconds to his lead at the Tour of California with victory in stage six.
The American, one of the sport's leading time-trial riders, made the most of his speciality to extend his lead over former Team Sky rider Michael Rogers to one minute, 47 seconds with two stages remaining.
Van Garderen, riding for the BMC Racing team, was last off start ramp after assuming the lead on Thursday and he was the only man able to break the 49 minute barrier on the tough 19.6 mile course that finished with a taxing climb.
He was one of few riders to use a specialist time-trial bike and his decision paid dividends with a time 23 seconds faster than closest rival Lieuwe Westra (Vacansoleil), who was the winner of last Sunday's opening stage.
Australia's Rohan Dennis (Garmin-Sharp) finished third, another five seconds further back, with Rogers (Saxo-Tinkoff) in fourth place, but his time of 49:57 was more than a minute behind van Garderen.
His likely toughest challenger, American time-trial champion David Zabriskie, was unable to start the sixth stage after crashing on a recon ride - he suffered a broken collarbone and will miss the defence of his title.
"There were never very many moments in the race to recover," van Garderen said.
"You started on a big climb, then up another climb, and the only time to recover was a technical descent, but you're holding your breath trying not to crash. The long straight headwind section was harder than the climb itself.
"I knew I could produce power on my time trial bike so I just put that out of the equation. I didn't reconsider my decision. It was a very interesting route the Amgen Tour of California chose. Very dynamic - had a little bit of everything."
The race is likely to be decided on Saturday's Queen Stage, which takes the remaining riders 91.4 miles from Livermore to the summit finish on Mount Diablo, although it will be tough for any of van Garderen's rivals other than Rogers to make up chunks of lost time from Friday's time-trial.