Former world champion Gilbert forged clear of a 15-man breakaway on the steep final third category climb to claim his sixth career Vuelta stage in the streets of Bilbao.

The 37-year-old winner of this season's Paris-Roubaix, who missed out on selection by his team for the Tour de France, came in clear of Spanish duo Alex Aranburu and Fernando Barcelo.

They were the only ones able to give chase to Gilbert, reducing the 19-second gap he'd established over the closing eight kilometres to three seconds.

"The atmosphere on the last climb was like at the classics, with all the flags. It was great, and boosted my motivation" said the stage winner.

"I've often ridden in the Basque country but I've never won here. It's a first and I'm thrilled as it's like Flanders here, they love their cycling," added Gilbert after his 10th Grand Tour stage success.

The Belgian, who is quitting Deuceninck-Quick Step for Lotto-Soudal this winter, appears to be coming to the boil at the right time for this month's world championships in Yorkshire.

Roglic meanwhile remains one minute 52 seconds ahead of Alejandro Valverde in the general classification ahead of Friday's 166.4-kilometre 13th stage with seven ascents including a fearsome final 'hors categorie' climb up Los Machucos.

"I'm not afraid of any stage especially as I've got a very strong team behind me," said Roglic, who finished with the other main contenders three minutes behind Gilbert.

He added: "It's an honour to wear the red jersey and I'll be the happiest of men if I've still got it in Madrid (on September 15)."

Placed third in the GC, 2mins 11sec adrift, is specialist climber Miguel Angel Lopez who said of Friday's stage: "Let's hope it's a great day".

"It's not all about Los Machucos," he noted, "there are lots of climbs before then. I'm hoping to have enough strength in the legs to do something good."