Arensman wins Vuelta stage 15, Evenepoel retains red jersey
Arensman attacked to catch and pass Marc Soler of UAE Team Emirates and pushed on to win alone on the "queen stage" to the altitude finish atop Sierra Nevada.
The Dutchman was the only rider from the breakaway who was able to resist Movistar rider Enric Mas, who came second after finishing one minute 23 seconds behind the winner.
"It's still really hard to believe, it really hasn't sunk in," said Arensman told Eurosport.
"When I was alone... I only kept thinking that I got to push and it was enough. It's unbelievable."
Miguel Angel Lopez of Astana Qazaqstan came third, while Quick-Step Alpha Vinyl rider Evenepoel finished 10th after coming under pressure early on the climb.
Evenepoel retained his lead but lost time to Jumbo-Visma's Primoz Roglic, who made an attack in the final kilometre and finished fifth.
Evenepoel remained 1:34 ahead of Roglic with Mas in third place, 2:01 behind.
After a rest day on Monday, the Vuelta a Espana will pick up again on stage 16, a 189km ride from Sanlucar de Barrameda to Tomares on September 6th.