Chris Froome is two days away from becoming the second British rider to win the race after Sir Bradley Wiggins last year.
Tour de France: Chris Froome zooms to cruise control
LE GRAND-BORNAND, France // Rui Costa won the mountainous 19th stage of the Tour de France with a solo breakaway on the final climb while Chris Froome stayed in yellow as expected attacks never materialised on Friday.
Costa secured his second stage win of the race after catching Frenchman Pierre Roland about a quarter of the way up the fourth and final major ascent of Col de la Croix Fry.
"A lot of Portuguese fans have supported me through this Tour and I want to thank them," Costa said through a translator.
German veteran Andreas Kloeden was second, 48 seconds behind, and Belgian Jan Bakelants was 1:44 back in third.
Froome and his main Tour rival Alberto Contador were still some distance behind Portugal's Costa when he clinched his third career Tour stage win.
The 204.5-kilometre trek featured two HC climbs and two Category 1 ascents between Bourg-d'Oisans and Le Grand-Bornand in the snow-capped peaks of the Alps.
Contador was tipped to attack Froome on the long downhill finish, but perhaps because of the rainy conditions, the attack never came.
Froome and Contador rolled over the line together, several minutes behind Costa, and Froome maintained his lead of 5:11 over the Spaniard.
"For us the objective was to stay on the wheel [of the other contenders]," Froome said. "The team did a huge amount of work today. There are still 125 kilometres to go tomorrow."
He is two days away from becoming the second British rider to win the race after Sir Bradley Wiggins last year.
"I didn't want to attack in the downhill," Contador said. "A lot of people like me and when they see me attacking downhill they get scared."
The Spaniard has only today's 20th stage from Annecy to Annecy-Semnoz to claw back his large deficit to Froome, who will likely look to stay safe so that he can match Wiggins' feat Sunday.
"It all depends on how my legs are tomorrow," Contador said."It depends how I feel."
Colombian climber Nairo Quintana is 5:32 behind in third overall.
Froome was not attacked up the first of the two big HC climbs to Col du Glandon. They are known as HC, Hors Categorie, because they are considered so tough they are beyond classification.
"There was a moment when I wanted to attack and thought about it, but then I thought it was best to reach the finish line with Roman," Contador said.
With the rain becoming heavier, Costa reached the top of the final climb and then negotiated a long and slippery descent of some 13 kilometres to the finish line.
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