Slovenian Primoz Roglic struck another blow in his bid to win the Vuelta a Espana by extending his overall lead by 33 seconds after finishing second on Friday's stage 13 on the tail of winner Tadej Pogacar.
Roglic now leads Spaniard Alejandro Valverde by two minutes 25 seconds, while Slovenian Pogacar climbed into third place overall thanks to his stage win, trailing Roglic by three minutes and one second.
Roglic had taken a commanding lead by winning Tuesday's time trial but had taken it easy in the last two hilly rides along with his fellow general classification contenders.
Yet he took centre stage when the race returned to the mountains in picturesque northern Spain for the 166.4 kilometre ride from Bilbao to Los Machucos. Monumento Vaca Pasiega, producing a stunning late double-pronged attack with Pogacar.
Twice winner Chris Froome once compared the stage's summit finish to "riding up a wall" and it was on the final ascent of the stage where the drama began.
Spaniard Hector Saez was leading by over two minutes before reaching the foot of Los Machucos but he was soon overtaken by Bruno Armirail as the climb kicked in, with the peloton closing in behind.
The 2016 winner, Nairo Quintana, launched a short-lived attack but was soon reeled in, while Roglic and Pogacar finally broke free with two kilometres to go.
The Slovenian duo then set their sights on the then leader Pierre Latour, soon overtaking the Frenchman with little more than a kilometre to go.
Twenty-year-old Pogacar dug deeper and took his second stage victory of this Vuelta, his Grand Tour debut, while Roglic came in right behind in his slipstream, with Frenchman Latour finishing third, 27 seconds back.
Valverde and Quintana were fourth and fifth respectively, also 27 seconds down, while Miguel Angel Lopez finished one minute and one second behind Pogacar and Roglic, dropping to fourth overall.