Chris Froome survived another barrage of mountains and rain-soaked descents to retain his Tour de France lead as breakaway rider Rui Costa soloed to a second victory of the race on stage 19.
Froome was able to stay with his closest rivals over the 204.5km day's five categorised climbs and then avoided incident on two treacherous downhill sections on the way to the finish line in Le Grand-Bornand.
The result means he takes a 5min 11sec lead into Saturday's final Alpine stage and it appears only a catastrophe can deny him overall victory in Paris on Sunday.
Movistar's Costa, meanwhile, followed up his win on stage 16 by attacking his fellow escapees on the final climb of the day, 21km out, and then hanging on down the drenched descent to beat Andreas Kloden (RadioShack-Leopard) by 48 seconds, with Jan Bakelants (RadioShack-Leopard) taking third.
Contador falls short
Froome crossed the line 8min 40sec after Costa in 25th place in a group also containing Alberto Contador (Saxo-Tinkoff), Nairo Quintana (Movistar) Roman Kreuziger (Saxo-Tinkoff) and Joaquim Rodriguez (Katusha), all of whom failed to put serious pressure on the yellow jersey during an arduous day that offered plenty of opportunity.
Saxo-Tinkoff placed a man in the day's breakaway and also rode on the front of the peloton for much of the stage, but although they successfully dropped the majorty of Froome's team-mates, neither Contador or Kreuziger attacked the Briton in a display that suggested they have given up hope of overhauling his lead.
Only Rodriguez tested Froome, with an attack on the last climb, the category-one Col de la Croix de Fry, as rain began teeming down, yet he was unable to maintain his injection of pace and was swiftly reeled back in.
The relative lack of action in the peloton gave the breakaway riders free rein to battle for victory between themselves, and it was a compelling narrative fought out for much of the day.
No fewer than 44 riders got into the initial escape, but then Ryder Hesjedal (Garmin-Sharp) moved into the lead with first Mikel Nieve (Euskaltel-Euskadi) and later Pierre Rolland (Europcar) on the day's two opening climbs, the hors-categorie Col du Glandon and Col de la Madeleine.
Rolland attacked on the third climb, the Col de Tamie, to drop Hesjedal and also led over the subsequent Col de l'Epine as he moved to within one point of Froome at the top of the mountains classification.
But with a clutch of other escapees still chasing him down, his chances of staying out to the finish were slim and when Costa attacked on the Col de la Croix de Fry, the Frenchman's game was up.
In similar style to his win in Gap on Tuesday, the Portuguese rider swiftly opened up a healthy gap and then defended it with a diligent descent to continue his impressive race and add a third Tour stage win to his palmares.
Stage 19 result
1 Rui Costa (Por) Movistar, 5.59.01
2 Andreas Kloden (Ger) RadioShack-Leopard, +0.48
3 Jan Bakelants (Ger) RadioShack-Leopard, +1.44
4 Alexandre Genez (Fra) FDJ, +1.52
5 Daniel Navarro (Spa) Cofidis, +1.55
6 Bart de Clerq (Bel) Lotto-Belisol, +1.58
7 Robert Gesink (Ned) Belkin, +2.03
8 Alessandro De Marchi (Ita) Cannondale, +2.05
9 Mikel Nieve (Spa) Euskaltel-Euskadi, +2.16
10 Ruben Plaza (Spa) Movistar, +2.44
Selected others 23 Alberto Contador (Spa) Saxo-Tinkoff, +8.40
25 Chris Froome (GB) Team Sky, same time
1 Chris Froome (GB) Team Sky 77.10.00
2 Alberto Contador (Spa) Saxo Tinkoff, +5.11
3 Nairo Quintana (Col) Movistar, +5.32
4 Roman Kreuziger (Cze) Saxo-Tinkoff, +5.44
5 Joaquim Rodriguez (Spa) Katusha, +5.58
6 Bauke Mollema (Ned) Belkin, +8.58
7 Jakob Fuglsang (Den) Astana, +9.33
8 Daniel Navarro (Spa) Cofidis, +12.33
9 Alejandro Valverde (Spa) Movistar, +14.56
10 Michal Kwiatkowski (Pol) Omega Pharma - Quick-Step, +16.08
- Green (points classification): Peter Sagan (Svk) Cannondale
- White (best young rider): Nairo Quintana (Col) Movistar
- Polka dot (mountains classification): Chris Froome (GB) Team Sky