Italy's Giulio Pellizzari celebrated "the best day of my career" when upstaging the big guns in Wednesday's Vuelta a Espana 17th stage as Jonas Vingegaard retained the leader's red jersey.

The 21-year-old crossed the Alto de El Morredero summit finish 16sec clear of Briton Tom Pidcock.

Pellizzari's Australian Red Bull Bora teammate Jai Hindley took third ahead of Vingegaard.

Danish race favourite Vingegaard goes into Thursday's time-trial with a 50sec cushion in the general classification over Joao Almeida, who finished the stage in fifth.

Organisers later announced they had shortened the race-against-the-clock in Valladolid from 27.2km to 12.2km for security reasons in the face of the pro-Palestinian protests that have targeted the last of cycling's big three races.

Wednesday's stage passed off without incident but a large number of protestors are expected to demonstrate on Thursday against the presence of the Israel-Premier Tech team.

"In order to provide greater protection...the organisation of La Vuelta, in coordination with the Valladolid City Council and after consulting with the Jury of Commissaires, has decided that tomorrow's time trial stage will take place over a 12.2 km route, maintaining the originally planned start and finish," stated La Vuelta.

The race finishes on Sunday in Madrid with heightened security planned in the Spanish capital.

Meanwhile the leaders cancelled each other out on the scorched and wind-swept slopes of Alto de El Morredero after a gruelling 143.2km ride from O Barco de Valdeorras, with Pellizzari seizing his chance.

"Over the last three kilometres I said to myself 'the time has come to go'. This is the best day of my career," he said.

Vingegaard was thankful to survive the day still in red.

"I wasn't feeling 100 percent, but I did what was required," said the rider still feeling the exertions of chasing home Tadej Pogacar in the Tour de France in July.