Porte chased down an attack by Chris Froome (Sky) on the descent, which will be used in the upcoming Tour de France. The two raced into La Motte-Servolex with Astana's Fabio Aru and Jakob Fuglsang, who won the sprint.
"There were a lot of attacks [on the climb], but our team stayed calm," Porte explained. "I was happy to come over the top with just Froome and I, and Aru in front with Jakob.
“It was a good stage, a crazy descent, but I'm in a good place."
Porte leads the overall by 39 seconds on Froome. Fuglsang is at 1-15 and other favourites like Alejandro Valverde (Movistar) and Romain Bardet (Ag2r) lost time.
The 8.7km climb in southeast France averages 10.3 per cent. Porte had Nicolas Roche and others working to keep him in front when previous leader Thomas De Gendt (Lotto-Soudal) faded. With Froome, they kept Aru at a manageable 12-second gap over the top with 15.5 kilometres to race.
Froome led out, Porte accelerated on the right by the barriers, but Fuglsang succeeded to the left.
"It's nice to have the jersey, but I know the next two days are going to be super hard," Porte said. "I feel up for it. I think we have the team here to try to finish it off on Sunday."
Fuglsang notched his first victory since 2012 and Astana's second of the 2017 season, following Michele Scarponi's win in the Tour of the Alps in April.
"It's been a bit of bad luck for our team," Fuglsang said. "Luckily we are competitive now before the Tour.
"To go in the Dauphiné like this, and on the first hard stage. To be there in front with two of the other favourites for the Tour.
"Also, for the Dauphiné it's really nice. For me personally to win for the first time for Astana... It's a huge relief, a huge relief."
The weight fell on Astana's shoulders with two men in the four-man front group. Aru played his card on the ascent, Fuglsang chased Froome on the descent. In the sprint, Aru gave the faster Fuglsang a lead-out.
"It's a success of the team, not only Fabio and me, but the guys who worked before the climb and kept us in position to make it as easy as possible. Also, they were there and protecting and helping. It's a victory for the whole team, for sure."
Thank you for reading 20 articles this month* Join now for unlimited access
Enjoy your first month for just £1 / $1 / €1
*Read 5 free articles per month without a subscription
Join now for unlimited access
Try first month for just £1 / $1 / €1