Geraint Thomas ticked off the final mountain test on the Tour de France and snatched six bonus seconds to extend his lead in yellow as Sky team-mate Chris Froome slipped off the podium two days from Paris.
Primoz Roglic took victory on stage 19 to Laruns by 19 seconds, enough to propel the Slovenian above Froome into third place overall going into Saturday's decisive time trial.
Thomas was second on the stage, nabbing six bonus seconds to extend his lead over closest rival Tom Dumoulin to two minutes and five seconds.
With his own bonus seconds applied, Roglic moved into third place, 13 seconds ahead of Froome who slips to fourth, two minutes and 37 seconds behind Thomas.
Team Sunweb's Dumoulin may be the world time trial champion, but Thomas will be confident of defending his advantage in Saturday's 31-kilometre race against the clock which will settle the general classification fight.
This was the stage that worried Team Sky more - a 200.5km test from Lourdes that included over 5,000 metres of climbing and took on the Aspin, Tourmalet and Aubisque.
The race came to life at the foot of the Tourmalet, as Ilnur Zakarin of Katusha-Alpecin attacked and drew out Movistar's Mikel Landa, AG2R La Mondiale's Romain Bardet, and Bora-Hansgrohe's Rafal Majka.
Sky looked unruffled but over the course of the Tourmalet's 17km, at an average gradient of 7.3 per cent, the group pulled more than two minutes clear, and that advantage only grew as they caught the day's breakaway on the descent.
What a ride from @GeraintThomas86. Faultless in the mountains, he sprints to second place, taking six bonus seconds and extending his race lead ahead of tomorrow's deciding time trial #TDF2018 pic.twitter.com/eogQxgY3PH— Team Sky (@TeamSky) July 27, 2018
Landa was second on the virtual classification at that point, within 80 seconds of yellow, but their advantage would begin to dwindle as they started to attack one another on the Aubisque.
As the yellow jersey group closed in on those up the road, Roglic's LottoNL-Jumbo team-mate Steven Kruijswijk and then Dumoulin launched attacks to test Thomas.
The Welshman was quick to respond but Froome looked in trouble, at one point dropping a full 30 seconds behind as his legs span furiously and his tongue hung out.
The four-time Tour winner needed the help of the tireless 21-year-old Egan Bernal to pace back on, and as he caught the yellow jersey, Landa and Bardet were being brought back.
A terrifying descent followed as they raced down the mountain in poor visibility. It was in the mist that Roglic attacked, the former junior world ski jump champion launching from the side of the mountain to move into the podium places.
Thomas looked in control as he followed his team-mate down the descent and then, as has become his style in this Tour, he produced a sprint in the final few hundred metres, hoovering up the six bonus seconds that come with second place to pad what looks to be a commanding lead.
World champion Peter Sagan, struggling hugely after a nasty crash on Wednesday, was dropped on the Col d'Aspin and looked in a world of hurt as he hauled himself over the climbs.
However, the Bora-Hansgrohe rider, needing simply to make it to Paris to win the points classification, made it inside the time cut - more than 38 minutes down - and now looks set for a sixth career green jersey.