Geraint Thomas will “expect the worse” as he prepares to see off his Tour de France rivals for perhaps the final time on Friday afternoon.

The Welshman heads into the mountains for the last occasion before Saturday’s time trial, with a lead that most expect him to be able to protect but there are no guarantees.

Thomas and Team Sky will be alive to attacks from all his rivals as he seeks to retain his one minute 59 second advantage over Team Sunweb’s Tom Dumoulin –  an advantage preserved on yesterday’s flat stage to Pau  which won by Frenchman Arnaud Demare –  as attention turns to Stage 19.

An imposing route will take the riders over three-quarters of the ‘Circle of Death’ as they tackle the Aspin, Tourmalet and Aubisque on a 200km stage from Lourdes to Laruns, and fireworks are expected before tomorrow’s time trial provides the final sort-out in the general classification.

“We’re expecting the worst and hoping for the best,” Thomas said. “We’re expecting a lot of attacks straight from the gun, to go in the break or maybe on the Tourmalet half-way through and certainly on the last climb.

“It’s the last mountain stage and I think guys will try to take any opportunity they can. But in the back of their minds they have still got to have the time trial. They can do a big move and maybe gain two or three minutes and quite easily lose a chunk of time in the time trial.”

Thomas will have the rare luxury of having four-time Tour winner Chris Froome ride in his service after his team-mate slipped to third overall.

“Obviously having ‘Froomey’ at my disposal is phenomenal,” Thomas said. “But hopefully he won’t have to do much. It will be a big test (for me) but I think it’s more one for the team to control. The last climb will be down to legs. It will be good to keep doing what we’ve been doing.”

Yesterday was uneventful for most of the 171km. Groupama’s FDJ’s Demare was able to hold off Christophe Laporte (Cofidis) and Alex Kristoff (UAE Team Emirates).

As befits a team that plans for every eventuality, there will be no complacency. It’s just a few weeks since fellow British cyclist Simon Yates took a solid advantage into the 19th stage of the Giro d’Italia and ended up losing 40 minutes on his rivals, the exertions of the days before catching up with him at the worst possible moment.

But Dumoulin will feel he needs to take at least a minute off Thomas’s advantage heading into the time trial, a discipline in which he is the reigning world champion.

All of which leaves 231km ahead of toil on the tarmac that contains more questions than answers.