Team Sky's star won the stage deep in Italy's northeast ahead of race leader Simon Yates (Mitchelton-Scott) in pursuit. The turnaround victory comes after two crashes and losing time in stages in the 2018 race.
"I am really, really happy with the victory today," Froome said. "It's a big boost of morale after what's been a tough start for the race for me and the team."
Froome crashed in training ahead of stage one in Jerusalem and again on wet roads back in Italy. The falls, both on his right side, saw him struggle. He said that he felt at his worst on a day last week during an insignificant flat sprint stage.
Yates still commands the race overall with 1-24 minutes over Tom Dumoulin (Sunweb). Froome, however, jumped from 12th overall to fifth and sits at 3-10 minutes back with many mountain stages remaining in the coming week, but also a 34.2-kilometre time trial.
"It's a great boost for us, but at same time, to be realistic, I am still three minutes down on GC," he continued.
"There are some really strong riders here. Simon's done an amazing ride up to now. Even in the last kilometre today, I thought he was going to catch me. He's got more of a kick than me, I thought he was going to come flying around me… it was such a nice feeling to reach those last few hundred meters and not have him on the wheel.
"I really want to thank everyone who's supported us especially through this first part of the race where it's been hard. A special day for us and a memorable victory for me on top of the Zoncolan, one of the most iconic climbs in Italy."
The iconic 10.1-kilometre run in the Italian Dolomites averages 11.9 per cent and touches 22 per cent in parts. Fans enjoyed a day out on the climb and military proudly lined the final kilometres.
Froome, to be ready, previewed the climb a month ago in training ahead of the Tour of the Alps. That, and of course his legs, may have made the difference.
"I saw Santa Claus earlier! I thought I was hallucinating at one point!" Froome said.
"It was very, very special, so much planning went into this stage, it was always my objective to build into this race and reach this point very strong – unfortunately, I've lost a lot of time earlier.
"Racing on the climb, having a plan a mind and knowing where the easier sections were… Wout Poels setting a high tempo on earlier slopes and stringing things out. I didn't have to accelerate much to get a gap, it was already very high.
"The fans were great. That dinosaur got a little bit close just have to move him out of the way a little bit! The atmosphere has been incredible, have to say grazie mille to all the tifosi, they make the race what it is."
Froome became only the sixth winner in the climb's short history. Organiser RCS Sport introduced it in 2003 and it has been a hit since.
Thank you for reading 5 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