Sánchez, the Astana rider who won the road race gold medal at the Baku 2015 European Games, attacked on the final climb of the 144 kilometres stage from Etxebarria along with Confidis' Navarro.

He then produced a burst of speed to claim his second victory of the year in a time of 3hours 54min 21sec following a stage win during February's Volta ao Algarve.

The peloton was closing fast on the two leaders and, had he been given an extra 10 metres, Australia's Simon Gerrans may have taken victory as he rapidly accelerated.

He eventually finished third for Orica-GreenEdge.

Italy's Fabio Felline finished fourth and Australia's Simon Clarke fifth as some of the biggest favourites for the overall title finished further down the field.

This included Spain's Tinkoff rider Alberto Condador and Colombian Movistar rival Nairo Quintana, who each crossed the line together in 24th and 26th place respectively after testing each other on the climbs.

Contador is a three-time former winner who triumphed most recently in the stage race - also known as the Tour of the Basque Country - in 2014.

Quintana won the 2013 edition.

Katusha's Spanish defending champion Joaquin Rodriguez placed 37th today but was also awarded the same time as the winner in a congested finish.

All three will seek to make a move tomorrow in a 174.3km stage culminating in a climb to the finish line in Baranbio-Garrastatxu.