Thursday's stage 4 test, which featured six categorised climbs in the final 60km of the day, included the summit finish on the Col de la Croix de Chaubouret, a 10km climb with an average grade of 6.7 percent.
Thomas eventually finished second to teammate Richie Porte, with the pair crossing the line nearly together. World champion Michal Kwiatkowski (Etixx-QuickStep) came in eight seconds later for third, holding the overall lead for another day. Van Garderen finished 17 seconds behind Porte and climbed to fourth overall, 27 seconds behind Kwiatkowski.
“The legs felt good,” van Garderen said of the hilly stage. “I was a little bit isolated with Sky having so many strong guys up there. I did what I could. Hats off to Sky. They really rode a great race, but I feel good and we're looking forward to Saturday and Sunday."
Friday's stage 5 starts with the category one climb up the Col de la République. After a 40km descent, the stage traverses the lumpy roads of the Ardèche and Drôme regions before ascending three climbs in the final 70km of the day before the finish in Rasteau.
Stage six on Saturday will be another tough day. The 180.5km stage starts in Vence and finishes in Nice after covering six categorised climbs, three of them category one. The last climb of the day is the 653-metre high Côte de Peille with 25km left to race, then a rapid plunge into Nice.
“Saturday I know the course very well,” van Garderen said. “It's not a summit finish, but it's a very hard day, and if it rains then it adds another element and we'll be looking to ride aggressive.”
The race returns to the traditional denouement up the Col d’Éze for the final stage on Sunday. Though not the steepest of climbs, the Col d’Éze has the potential to shake up the general classification. The hardest part of the climb is the first two kilometres, where the road averages 7.7 percent, then 8.5 percent before flattening out near the finish.