Launching an incredible long-range attack with 80 kilometres remaining, the Team Sky rider crested three climbs solo on the race’s queen stage and pulled on the maglia rosa with an advantage of 40 seconds.
A perfectly executed race strategy saw Froome overturn a two minute and 54-second deficit, with his team-mates setting a searing pace on the Colle delle Finestre, laying the foundations for a memorable attack.
Froome’s solo mission saw the gap extend out gradually, with overnight leader Simon Yates (Mitchelton-Scott) distanced and chief rival Tom Dumoulin (Team Sunweb) gradually slipping back over the Sestriere and Bardonecchia ascents.
Chased by a group of Dumoulin, Thibaut Pinot (Groupama-FDJ), Richard Carapaz (Movistar), Miguel Angel Lopez (Astana) and Sebastien Reichenbach (Groupama-FDJ), Froome claimed pink on the road ahead of the final first-category peak, as his advantage spun out over three minutes.
After the stage Froome tried to put an incredible day into words: "I don’t think I’ve ever attacked with 80 kilometres to go before like that, on my own, and gone all the way to the finish. The team did such a fantastic job to set that up for me. It was going to take something really special today to first of all get rid of Simon [Yates], then Dumoulin and Pozzovivo. To go from fourth to first, I wasn’t going to do that on the final climb alone, so I had to try something from far out.
"Colle delle Finestre was the perfect place to do it. Gravel roads remind me a little bit of riding on the roads back in Africa. I felt good and thought it was now or never - I have to try.
"There’s a really hard day tomorrow but the legs are feeling good and I’ve been feeling better and better as this race has gone on. Even today out front, I gave it everything, but I also tried to stay within my limits and tried to stay within myself. Hopefully we can finish this off tomorrow."
"It was a case of now or never - we had to go for it.", said Froome.
Froome's exploits also saw him climb his way into the blue mountains jersey, and helped Team Sky solidify their grip on the team classification in Italy. Courtesy of leading the race over the Finestre he also claimed the Cima Coppi prize at the highest point of the race.
Froome's team-mates played a key role in turning the race upside down. Early on Sergio Henao and David de la Cruz were piling on the pressure as part of an early break on the Colle del Lys.
The action really ramped up on the early slopes of the Finestre, with Salvatore Puccio and De La Cruz setting a tempo, before Kenny Elissonde ripped the group apart. Shortly after Froome launched his winning move, 80km from home.
After jumping out of the team car, a thrilled Sport Director in Nicolas Portal gave his views.
He told Eurosport: "We forget that it’s Chris Froome. We believed it could happen. We’ve been pushing Froomey, he never wanted to stop. He wanted to fight until the end and it shows how strong he is. It’s unbelievable.
"Most of the time we are more defensive because in general we have had the jersey but here we have been in a different situation and he’s needed to build his form because he had the crash and things like this. The way the team executed the plan today and yesterday, we saw a little bit of weakness in some of the GC contenders and the team has been feeling stronger and stronger, Froomey was feeling good as well, so we said all or nothing on Colle delle Finestre. It was unbelievable."
Team Principal Dave Brailsford was quick to pay tribute to the total team effort that went into Friday's queen stage.
Unsurprised to see his team leader in pink, he told Eurosport: "We spent all day yesterday really dissecting the stage, looking where everybody was at. The plan was always for Chris to come good in this little block, and the Finestre was going to be decisive. We thought maybe it was a little too far out but you’ve got the 27 hairpins at the bottom and that’s where the guys put it on the line and split the race up.
"Today was about fuelling, and making sure that you can fuel a ride like this all the way through to the end. It’s fundamental. So all the members of staff, myself included, have been out on the side of the road, and we put in place a fuelling plan for him to make sure that he would not miss a beat. That’s basically the game changer.
"Knowledge isn’t the thing. It’s the final step in sport that makes the difference, that little detail of ‘how do you make it happen?’ Thankfully the staff got out today and did a fantastic job, every single one of them - and he delivered.
"First thing's first it’s all about recovery. It’s about who recovers the best for tomorrow and that’s going to be the determining factor for this race quite frankly. Obviously we don’t need to gain any time and normally we race not to lose any time, not to gain time, so it’s going to be a difficult start I imagine, but I prefer to be in this situation at half-time than not!
"Today was probably the best performance of (Froome's) career. One of the best performances, and one of the best days in the team’s history today. Taking it on and being able to animate it like that is fantastic. It’s only a job half done now. We’ll see what happens tomorrow."
Stage 19 result:
- Chris Froome (Team Sky) 5:12:26
- Richard Carapaz (Movistar) +3:00”
- Thibaut Pinot (Groupama-FDJ) +3:07”
- Miguel Angel Lopez (Astana) +3:12”
- Tom Dumoulin (Team Sunweb) +3:23”
- Chris Froome (Team Sky) 80:21:59
- Tom Dumoulin (Team Sunweb) +40"
- Thibaut Pinot (Groupama-FDJ) +4:17"
- Miguel Angel Lopez (Astana) +4:57"
- Richard Carapaz (Movistar) +5:44"