The Team Sky rider held off a spirited series of attacks by defending champion Tom Dumoulin on stage 20 from Susa, retaining the pink jersey and stretching his lead to 46 seconds.
The 33-year-old need only negotiate today’s largely ceremonial stage in Rome to add the Giro to his victories in the Vuelta a Espana and the Tour de France, becoming only the third man to hold all three titles simultaneously. Eddy Merckx, in 1973, and Bernard Hinault nine years later are the only others to match Froome’s mastery of the general classification.
Froome appeared to be barely in contention a matter of days ago, but moved into the lead on Friday, when he made an audacious solo charge from 80km out on the mountainous stage from Venaria Reale to Bardonecchia.
It was a monumental effort which propelled him from three minutes and 22 seconds off the lead to the frontrunner by 40 seconds.
Dumoulin made several game but unsuccessful attempts at leaving Froome behind and ended up accepting his fate in the final phase of racing.
“It’s just an amazing feeling, could you see that outcome coming?” Froome told Eurosport 1. “That’s what it’s all about, making people dream. If you want to achieve something, you’ve got to believe in it first. I had this huge goal to try to achieve and I think once you really believe in it you’re 90 per cent of the way there. It has been such a brutal race, absolutely brutal, but it has been a beautiful, beautiful event.”
Froome’s adverse analytical finding for Salbutamol at the 2017 Vuelta may continue to rumble on without conclusion but in the absence of closure on that issue, he continues to build an astonishing list of achievements.
He has, of course, not acted alone and he paid fulsome tribute to his Team Sky colleagues for continuing to back him even when he was deep in the field with glory a seemingly distant hope.
“I have to say that was a really big part of being able to do what I did, everyone believing in me and buying into the one plan we had,” he said. “A lot of times when things don’t work out for general classification teams start falling apart, they lose breakaways and teams start doing their own thing.
“For the guys to say ‘we believe in you’ feels amazing. To be able to repay them after two and half, three weeks hard work feels amazing.”
Spaniard Mikel Nieve was the stage winner on his 34th birthday, but as the race moves to its conclusion it is Froome who will finish centre stage.