In 48 hours the cycling world will know for certain whether Geraint Thomas will roll into Paris as the second Welsh athlete to win the Tour de France after Nicole Cooke's exploits in the Grande Boucle Feminine back in 2006 and 2007.
Ahead of Thomas, 32, are two defining yet different form of examinations. The first, a 205km trawl through the Pyrenees that includes the Aspin, the legendary Tourmalet, the Col du Soulor and the rasping gradients of the Col d'Aubisque. The second assessment comes in the form of the shorter, but by no means less significant, 31km time trial to Espelette. On these two stages, Thomas' Tour will be decided and his career effectively defined.
The Team Sky leader's advantage over Tom Dumoulin (Team Sunweb) is a healthy 1:59, while third place Chris Froome (Team Sky) may be more concerned with the 16 seconds that separate him and the rampant Primoz Roglic (LottoNL-Jumbo), who can effectively throw caution to the wind in the face of the Team Sky machine over the next two stages.
"I think that we're expecting the worst and hoping for the best," Thomas said when he sat down for his post-stage press conference in Pau after stage 18.
"We're expecting a lot of attacks, from the gun, with riders going in the break and maybe even on the Tourmalet halfway through and certainly on the last climb."
Those likely to attack are Movistar and LottoNL-Jumbo, both with aspirations of breaking onto the Paris podium and winning stage 19 itself. AG2R La Mondiale will look to save their pride too, but Team Sky and Thomas' advantage throughout this Tour has been their depth. For example, two years ago Ian Stannard was a regular feature in the team's Tour arsenal. He has not ridden a Tour with Sky since, partly due to his form, but also because of the array of weapons Sky now have at their disposal.
Luke Rowe has managed to carry the workload of Gianni Moscon since the Italian's expulsion, and Michal Kwiatkowski, far from the rider he was in 2017, has still featured on the final climb of all but one mountain stage so far. Rowe, Kwiatkowski, Wout Poels, Jonathan Castroviejo and mightily impressive Egan Bernal all have a multitude of strings to their bow, and Thomas will rely heavily on his team's domination on Friday.
Froome's shift in position from leader to super domestique adds fuel to the Team Sky engine room, but while Thomas will be grateful for the additional support, he will be more than aware that the buck for winning the Tour this year will stop with him. If and when Roglic, Dumoulin and Movistar attack, it's the Welshman who must respond. He has been faultless in this year's race, both tactically and physically, but the final surge starts here.
"Hopefully we won't have to use Froome and we have strength in numbers and he's able to follow as well," Thomas said. "Obviously, having Froome at my disposal, so to speak, is just phenomenal, but hopefully, like I said, he won't have to do much anyway. It will be a big test. It's more for the team to control really. The last climb will be down to the legs, and it will be good to keep doing what we're doing.
"Obviously, it's the last mountain stage and guys will try and take every opportunity but at the same time, in the back of their minds, they still have the TT," Thomas said. "Do a big, big move tomorrow and maybe gain two minutes and then you can quite easily lose a chunk of time in the TT. It's that hard. It will be interesting, but we've been riding well the whole race, so hopefully, we can keep that going for one more day."
Geraint Thomas sits in the Team Sky train during stage 18 at the Tour de France. (Getty Images)
Race of truth
No one can predict the exact time gaps that we will see tomorrow, and perhaps the technical descent from the Aubisque will be the most significant factor in the race. The rolling time trial from Saint-Pèe-sur-Nivelle to Espelette favours Dumoulin, and the time trial world champion has form in taking time out of his rivals on his natural terrain. In a TT at the Tour in 2017 he put around 1:40 into Thomas, and in 2015, on the final mountain stage of that year's Tour, Thomas dropped from 4th to 15th. When asked about those incidents and potential omens, the maillot jaune batted them away.
"Not really. In the Giro, last year, I had a big crash and then lost 40 seconds to Dumoulin in the TT the next day," he said. "And then with regards to 2015, I was working every day in the wind and going full gas and emptying the tank most of the time. It's a totally different approach this time. You never know, but you try and stay confident and keep doing what we're doing. It's been working really well so far, so we'll try and keep doing that."
Earlier in the morning of stage 18, as Thomas rolled towards the sign-on, Cyclingnews caught up with the race leader, away from the mass huddle that has been a daily feature at the Team Sky bus. He was accompanied to the start by Rowe and seemed relaxed and ever more comfortable in yellow. This is new territory for him and for Sky, who have not worked for another leader at Grand Tour to this extent since the days of Bradley Wiggins.
"I'm really proud of that performance yesterday," Thomas said in relation to his ride up the Col du Portet.
"It was great for the morale and the confidence within the team. There are two more days and hopefully we can stay on the ball. Yesterday was probably a bigger performance for me in terms of GC than the two stage wins, I think, just because it was the last summit finish of the race and others wanted to try and gain time if they could. I gained time on everyone else, other than Quintana, and that was really encouraging.
"One more mountain stage, and we're going to get attacked on that last climb. Hopefully, I can respond to anything. Then it's the TT. I'm trying not to look too far ahead. I've just got to look at each day at a time."
Each day at a time but it's really the next 48 hours that will decide whose name is added to the maillot jaune history books.