Britain's Chris Froome was unable to close the gap on overall leader Juan Jose Cobo on stage 19 of the Vuelta a Espana from Noja to Bilbao.
The Team Sky rider remains second, 13 seconds behind with two stages left.
His Sky team-mate Bradley Wiggins stays third overall as Britain aim to put two riders on the podium of one of the three Grand Tours for the first time.
Igor Anton was the clear stage winner as the Vuelta returned to the Basque country for the first time in 33 years.
He finished the 99-mile (158.5km) ride in three hours 53.34 minutes, with second place going to Marzio Bruseghin of Italy 41 seconds back, while third-placed Dominik Nerz of Germany was one minute 30 seconds adrift.
Anton's runaway win did nothing to change the top of the overall leaderboard, however, with his fellow Spaniard Cobo still holding the advantage going into the final two days.
Saturday's 20th and penultimate stage will be 115 miles (185km) from Bilbao to the Basque capital of Vitoria, and is likely to be Froome's last chance to snatch the red jersey from Cobo.
Cobo said he was wary of the twin Sky threat from Froome and Wiggins in the last two stages.
"Today was a big step forward but it's not over yet," Cobo explained. "I'm sure Sky will keep attacking."
Froome, who started his cycling career as a mountain biker, said: "I've got nothing to lose and all to gain, so I went for it. Thirteen seconds is such a small margin it would be crazy to give the race to him."
Only one Briton has previously finished on the podium of a Grand Tour - Giro d'Italia, Tour de France, Vuelta a Espana - Scot Robert Millar was second in the Giro in 1987, after a second place in the Vuelta in 1986.
1. Igor Anton (Spain, Euskaltel) 3:53:34
2. Marzio Bruseghin (Italy, Movistar) +41secs
3. Dominik Nerz (Germany, Liquigas) +1:30secs
16. Chris Froome (Britain, Team Sky) +1:33secs
18. Bradley Wiggins (Britain, Team Sky) +1:33secs
1. Juan Jose Cobo (Spain, Geox) 77:59:12
2. Chris Froome (Britain, Team Sky) +13secs
3. Bradley Wiggins (Britain, Team Sky) +1:41secs