Soler blasted away from a fracturing lead group of some 10 riders with less than a kilometer to go in the 149-km second stage and claimed his first victory since 2007.
“I’m pleased to win because it’s been four years since I’ve won a race, and I was getting worried,” Soler told reporters.
“I’d had a tough first half of the season too, with lots of crashes and injuries. Finally, though, it seems like I’m back on track.”
Second behind the 28-year-old Movistar rider after a punishing Alpine stage was Italy’s Damiano Cunego, 12 seconds back, with last year’s overall winner Frank Schleck of Luxembourg in third on the same time.
“We’d talked about winning today’s stage in the team and agreed that I’d have to try in the last kilometer, but only my second attack worked,” Soler added.
“I knew if I didn’t get away then, it was over for me, because the slope eased a bit afterwards and guys like Danilo Di Luca could have caught me and passed me.”
Soler, winner of the 2007 Tour de France King of the Mountains competition, now leads with a slender 16-second margin over Cunego, whilst Dutchman Bauke Mollema lies third, 22 seconds back.
The Colombian dedicated the lead and the stage win to his team mate Xavier Tondo of Spain, who died in a domestic accident last month.
“This is for Xavier, who is no longer with us but who remains in our thoughts,” he said. “Apart from being a great rider, he was also a friend.”
Overnight leader Fabian Cancellara was dropped early on the second big Alpine climb of the day, the Aminona, while his Leopard Trek team mates piled on the pace for their main contender Frank Schleck, who whittled down the main group with a series of late attacks.
The race finishes next Sunday.