Pau - Yellow jersey holder Geraint Thomas is "expecting the worst", but warned ambitious rivals that going too deep on the final day in the mountains could end their Tour de France podium chances.
Thomas moved a step closer to becoming Wales's first Tour champion when he came through the 18th stage to Pau unhindered and with his lead of 1:59 on Dutchman Tom Dumoulin (Sunweb) intact.
Thomas had been lucky to escape being hauled off his bike by an "overexuberant" fan as he raced to third place at Saint-Lary-Soulan on Wednesday.
After avoiding such mishaps Thursday, the 32-year-old now only has to keep focus over a hilly 19th stage that features Pyrenean classics like the Col d'Aspin, the Col du Tourmalet and the Col d'Aubisque. And hope Team Sky do the rest.
"I think we're expecting the worst, hoping for the best," said Thomas.
"It will be a big test. I think it's one more for the team to control most of the day."
Yet Thomas has the race route in his favour as he bids to bring home Team Sky's sixth yellow jersey from the last seven editions, four of which have been won by teammate Chris Froome.
The finish line is 20km from the summit of the Col d'Aubisque, meaning any time his rivals may have gleaned over the stage's final, rolling 16.6 km ascent could, theoretically, be lost on the descent.
And efforts rivals spend trying to loosen his grip on a yellow jersey gained following back-to-back stage wins in the Alps could, he believes, be paid for in the penultimate-stage time trial over 31 km.
"It's the last mountain stage and I think guys are going to take any opportunity they can. But at the same time, in the back of their minds they still have to do the time trial," added Thomas.
"They could do a big, big move tomorrow (Friday) and maybe gain two, three minutes or whatever, and then quite easily lose a chuunk of time in the time trial.
"It's interesting, but we've been riding really well all race, and hopefully we can keep that going for one more day."
The biggest threat to Thomas comes from Dumoulin, who said: "If I see an opportunity, I'll take it."
But at nearly two minutes down, the Dutchman conceded: "My victory chances are slim... I would have to take something like two minutes off him, so it's complicated."
Former Sky rider Mikel Landa, now a rival with Movistar and hoping to lift teammate Nairo Quintana from fifth, warned: "Friday will be our day. It will be difficult, but tomorrow we hope to turn the race around."
Making Friday's stage more intriguing is the fact that Froome, who had been aiming for his fourth consecutive Grand Tour win, is now fighting for a podium place.
Third overall at 2:31 after losing second place to Dumoulin on Wednesday, the Kenyan-born Briton is in danger of losing his Paris podium place to those in his wake.
Slovenian Primoz Roglic, an ex-ski jumper who rides for Lotto-Jumbo, is 16 seconds behind him while Colombian climbing specialist Quintana is at 3:30.
"Having Froomey at my disposal, so to speak, is just, like, phenomenal," said Thomas.
"But hopefully, he won't have to do much anyway. I think the last final (climb) will be down to the legs.
"It would be good to just keep on doing what we've been doing."