In a tour de force on Thursday, Nibali blew away the peloton on a Pyrenees ascent too tough to be rated in Stage 18, all but locking up victory when the race ends in Paris in three days.
Nibali has combined racing smarts, skill at bike-handling, and powerful climbing legs to methodically piece together a lead of more than seven minutes, gaining seconds "here and there," as he put it after his fourth stage win.
That margin, if it holds, would be the second largest in 25 years: Jan Ullrich won by more than nine minutes in 1997. Armstrong won five of his seven titles from 1999 to 2005 by more than six minutes, but those victories were stripped after he was exposed as a doping cheat.
The last Italian to win the Tour was "The Pirate," Marco Pantani, in 1998. Nibali too knows about nicknames.
His family calls him Enzino. An attacking rider, he's been known as the "Shark of the Straits" in reference to the Strait of Messina off Sicily. One from his boyhood re-emerged on Thursday after the win at Hautacam resort: "Flea of the Pyrenees" — a nod to its first bearer, Vincent Treuba of Spain, decades ago.
Alexandre Vinokourov, general manager of Nibali's Astana team, said the Kazakh squad wanted the rider to show he deserved another. "We said, 'we need to show that there's a boss,'" Vinokourov said on French TV, recalling the team's game plan before Thursday's stage. He said the stage victory was "not by chance."
But Nibali wasn't impressed by the comparisons with the disgraced Armstrong.
"I came to the Tour with a good preparation and a good team. But I'm not a boss like Lance Armstrong was," he said through a translator. "Let's leave the past behind us. I'm very clear about myself."
As a "flag-bearer of anti-doping," he notes his career ascension has been gradual. He won the 2010 Spanish Vuelta and the 2013 Giro d'Italia, putting him on track to become only the sixth rider ever to win all three Grand Tours.
The Italian has worn the yellow jersey for all but two days: That was last achieved by Armstrong nine years ago.
Nibali's bid was made easier after the pre-race favourites, 2013 champion Chris Froome and two-time winner Alberto Contador, withdrew due to crash injuries. Nibali noted he was leading them when they quit, and crashes are part of cycling.
Riders tackled the famed Tourmalet pass — the highest Pyrenean peak in this Tour — before heading to Hautacam on Thursday. Both climbs are among the toughest in professional cycling.
On the big, final climb, Nibali broke out of the peloton, chased down breakaway riders, and rode solo in front for the last eight kilometres (five miles) uphill.
The emphatic win in the 145.5-kilometre (90-mile) leg from Pau to Hautacam, where Nibali padded almost two minutes to his lead, essentially reduced the race drama to who will join him on the podium on the Champs-Elysees.
"I didn't want to lose command. My goal was to win here," Nibali said. "The team worked really hard and this victory is for them."
Thibaut Pinot and Jean-Christophe Peraud advanced their hopes to give France its first podium finisher since 1997. They each gained just under a minute on Alejandro Valverde in the final climb, bumping the Spaniard to fourth.
Those three will battle it out for the bottom two podium spots.
Friday's stage is mostly flat and unlikely to alter the top standings. Nibali's lead is so big — 7 minutes, 10 seconds ahead of Pinot, and 7:23 on Peraud — that it would take a disaster for him to lose the lead before Sunday. Valverde is just two seconds slower than Peraud.
"Everything is possible," Valverde said. "Before, I was ahead, now I'm behind, but it's very tight. I'm pretty happy."