Geraint Thomas pledged to help team-mate Egan Bernal to Tour de France glory after seeing hopes of defending his title washed away in a landslide in a chaotic finish to stage 19 on Friday.
Organisers were forced to stop the 126.5km stage from Saint-Jean-de-Maurienne to Tignes 37km short of its destination after an intense hailstorm hit in the valley and sent a deluge of rocks and mud across the road.
They quickly declared that times would be taken from the top of the Col de l'Iseran, the highest point on this year's Tour, even though some riders were well on their way down the descent and others were yet to reach the summit.
Bernal had been the first over it, just ahead of Mitchelton-Scott's Simon Yates who was chasing what would have been a third stage victory.
Bernal had attacked out of the group of favourites after Thomas and then Jumbo-Visma's Steven Kruijswijk had made moves of their own in an ultimately successful attempt to shake off race leader Julian Alaphilippe, whose fairytale run in the yellow jersey finally ended.
The new general classification shows Bernal leading Alaphilippe by 48 seconds, with Thomas in third place, one minute 16 seconds down.
That was enough for Thomas to concede and throw his support behind the 22-year-old, who stands to become the first Colombian Tour winner and the youngest of the post-war era, all while riding only his second career Grand Tour after helping Thomas to victory last year.
"I haven't seen any GC but for sure he'll have a decent advantage over everyone else so we'll fully support him now," said Thomas, who will now hope he can move up on Saturday to give his team their first Tour one-two since 2012.
Thomas had been happy to sit on Kruijswijk's wheel on the Iseran as his team-mate got away, not repeating Friday's scenes where his own attack perhaps served to limit Bernal's gains on the Galibier. The Welshman may well have hoped to bridge over on a final climb which would have suited his strengths.
"It's all ifs and buts," Thomas said. "The main thing is we've got the jersey in the team now. We're in a great position. We've just got to go and finish the job off tomorrow."
Bernal perhaps showed his age when presented with the yellow jersey, bursting into tears, but a young rider who has sounded happy to defer to Thomas up to this point asserted his authority as leader after the stage.
Asked if he would allow Thomas to attack on Saturday's final mountain stage to Val Thorens, he said: "If he wants to do it, yes. But I think it will be crazy to do something like that in these circumstances...
"I think the team should be careful. Thomas is on the podium so I think it doesn't make a lot of sense to attack tomorrow."
Opportunities for anyone to attack will now be extremely limited, with organisers announcing late on Friday that stage 20 would be shortened from 130km to just 59km, due to the "difficult weather conditions expected and the landslides noticed".
Several riders, not least Alaphilippe, had looked frustrated as they were brought to a halt in Val-d'Isere. Kruijswijk later described it as "a bit s***".
Thomas was seen in conversation with Tour director Christian Prudhomme, who could only gesticulate that there was nothing he could do with diggers attempting to clear a path up ahead.
Ineos team principal Sir Dave Brailsford said he had mixed feelings about taking the yellow jersey in such circumstances, but insisted it was reward for the way his team approached the stage.
"Fortune favours the brave at the end of the day," said Brailsford.
"We were always going to take today on and I thought the guys rode really well, to be honest...
"We don't control the weather. In one way, I'm really happy but in another way, I'm still really concerned for everyone else out there."
Asked if the weather had helped his team win the Tour, as now seems likely, Brailsford replied: "It didn't. No, we'll win the Tour de France because of how we ride."
It proved a brutal day for French fans, and not just those waiting in Tignes for a race that never arrived.
As Alaphilippe's grip on yellow was finally loosened, Thibaut Pinot's dream of becoming the first French winner of the Tour de France for 34 years was ended in cruel circumstances when the Groupama-FDJ rider was forced to abandon just 36 kilometres into the stage, having been fourth overall.
His team revealed later he had been suffering with a muscular injury first suffered on Wednesday's stage to Gap when he struck his leg with his handlebar when trying to avoid a crash, with the problem only growing worse.
"I did all I could," a tearful Pinot said. "I believed I might have had a chance (of continuing), that it would pass. But unfortunately, it did not.
"I was convinced (I could win), but unfortunately now I will never know. It will be hard to get over this."