Thomas took the overall leader's blue jersey on Friday when he finished fourth behind winner Primoz Roglic (LottoNL-Jumbo) on stage three to Trevi, central Italy, with Froome third in the general classification just three seconds behind his Welsh team-mate.
"I am in the best place obviously, but with tomorrow's long mountain finish, I'd bet on Froomey," Thomas said.
"We'll see how the legs are, but we were bit unsure of how we were, but we are both pretty good it seems. I hope to keep the jersey, but if I don't have the legs then hopefully Froome can take over."
Adam Yates (Mitchelton-Scott) placed second, Thomas fourth and Froome, after Team Sky's work in the technical final, 12th. Thomas moved into the lead on countback over Greg Van Avermaet (BMC Racing), three seconds ahead Froome in third. Sky's Michal Kwiatkowski sits fifth overall.
"I didn't expect to be in this position, and that's nice. The team has yet to win this race, and with myself, Froomey and Kwiat in good positions, hopefully one of us can do it."
Thomas says that the "first big test" will be stage four's 11.75km summit finish to Sassotetto.
Froome appears to be the team leader as he builds up for the Giro d'Italia in May. Today, all six of his team-mates rode for him on the undulating roads around the hilltop town in Umbria. Near the final, however, he was slightly distanced and Thomas rode ahead.
"I was full gas, the race was absolutely on at that point [when the gap opened] and the gaps were opening up all the place," Froome said.
"I didn't really know what to expect for the final today, such a steep kick to the finish, but it's a good result for us. G in the lead, me in third and Kwiato in fifth – it gives us a good position going into the queen stage.
"We'll see [tomorrow], it's still early days, this is part of my build up [for the Giro]. I'm not at my best yet, but on my way there."
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