Defending champion Primoz Roglic retained the overall lead as Belgian Jasper Philipsen on Thursday won the Vuelta a Espana's 15th stage, the longest of the race at 230.8km.

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Slovenian Roglic kept hold of the red jersey ahead of Richard Carapaz after a rain-sodden ride in north-western Spain on the longest day of the three-week Grand Tour.

Jumbo-Visma's Roglic has a 39-second advantage over Ineos' Ecuadorian rider, with Hugh Carthy 47 seconds behind with Friday to see a 162km hilly stage from Salamanca to Ciudad Rodrigo.

"It was a hard day. I'm really happy that now it is behind us," Roglic said.

"I don't know how much it was enjoyable, it was a hard pace, it was fast all day long and the cold and rain - a big and tough day behind us," he added.

Philipsen claimed his first Grand Tour stage success by pipping Pascal Ackermann at the line, with Jannik Steimle in third.

"I can't describe how happy I am. It means a lot for me. I've been waiting all of the Vuelta for this moment, it was unexpected," 22-year-old Team UAE Emirates' rider Philipsen said.

"It was a really strong breakaway. In the end I started believing it more and more but at the beginning of the day I never expected a bunch sprint," he added.

The red jersey standing times were taken with 3km left because of a reported oil slick near the finish line close to the border with Portugal after a mistake-free day for the contenders.

Tight Finish

An early group including previous stage winner Tim Wellens broke after 55km approaching the Alto de San Amaro as Roglic and his challengers crew avoided any trouble by staying together.

The pace stayed high despite humid conditions on an arduous day before Italian Mattia Cattaneo made his solo shot for glory with 30km left.

He stretched his lead to 90 seconds at one point on the Alto de Padornelo descent ahead of a flat finish and a head wind before arriving at the finishing line near to the Portuguese border.

Despite his efforts, the chasing pack, including Philipsen, cut down the lead in heavey fog as organisers announced the overall race times would be taken with 3km to go.

Philipsen split and edged German pair Ackermann and Steimle on the flat finish.