Porte, now with BMC Racing, put time on most of his rivals for the podium spot behind Froome in the 17-kilometre mountain time trial. He slipped to five minutes behind Froome, but moved within 1-08 minutes of Bauke Mollema (Trek-Segafredo) in second and 44 seconds of Adam Yates (Orica-BikeExchange) in third.
"Richie Porte did a good time trial today, strong, and yesterday he was the only one to make the race," Froome said after putting on a new yellow jersey.
"He looks like the one with the most to gain over the next couple of stages. Obviously, he had some bad luck in the early stage [with a puncture], it's a shame, but if he continues in this way, he'll see himself on the podium in Paris."
Porte lost 1-45 minutes due to a puncture in the second stage of the Tour, but improved since. Yesterday to the Finhaut-Emosson summit finish, he was the only one of the stars to make a significant attack.
Chris Froome follows Richie Porte stage 17 of the Tour de France (Watson)
(Image credit: Watson)
Today, the 31-year-old Australian clocked 31-16 minutes, just a fraction of a second slower than Fabio Aru (Astana) on the same time. Froome won the stage ahead of Tom Dumoulin (Giant-Alpecin).
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"Today was a good performance, it's just hard to think about the second stage and the time I threw away there," Porte said behind the podium.
"I had a good time trial. I showed that I'm climbing well. We did the recon on it, I knew it was a hard stage and it suited me.
"I took some more time out of some of the other GC guys. The next two days will be a big battle. I'm looking forward to taking my chance and fighting for the podium."
The next two days in the Alps are the final two testing days in the 2016 Tour before the flat stage into Paris. The 19th stage on Friday finishes with a climb up to Le Bettex below Mont Blanc. On Saturday, the stage covers the Joux Plane and descends to Morzine.
The Tour should see a good fight with only 1-08 minutes between second and sixth place.
"The podium is just so tight, other teams can't let other GC guys go either. I need to look at later tonight with the sports directors to see where we can peg some time back," added Porte.
"I'm confident for the next two days and the big mountains, hopefully I'll have space to take more time out of the big GC guys.
"I just want to have the days [to do it]. It's no secret I want that podium and I'm prepared to fight."
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