Nibali (Astana) added victory on the 145.5-kilometre 18th stage from Pau to Hautacam to wins in Sheffield, La Planche des Belles Filles and Chamrousse.
The Italian — the first yellow jersey holder since Eddy Merckx in 1974 to win four stages outside of time trials — began the day with an advantage of five minutes 26 seconds and enhanced his lead to a near-unassailable 7mins 10secs with just three stages to go.
Bar a major blow, he will win the yellow jersey in Paris on Sunday.
Nibali said: “It’s fantastic to have won four stages. I didn’t believe I’d do that.
“There aren’t many stages till the finish now and my lead is consolidated. I’m pretty serene.
“I’ve wanted to leave a footprint in the Pyrenees. I wanted to show that I’m the strongest, I wanted the stage win.”
Nibali’s Astana team boss Alexandre Vinokourov said: “Vincenzo wanted to prove he was the boss. He really wanted to win that stage.”
Nibali (Astana) added victory on the 145.5km 18th stage from Pau to Hautacam to wins in Sheffield, La Planche des Belles Filles and Chamrousse.
Frenchman Thibaut Pinot (FDJ) was second on the stage, 1min 10secs behind Nibali, to move up to second place overall.
Alejandro Valverde (Movistar), who began the day second, finished 10th, 1:59 behind, to drop to fourth overall, 7:25 behind Valverde.
Pinot is second by 13 seconds from Jean-Christophe Peraud, who was fourth on the stage, with Valverde two seconds further back.
Ireland’s Nicolas Roche was 29th on the stage, 8:55 behind. The Tinkoff-Saxo rider now lies 39th overall, 1:55:52 behind.
Today’s stage is the 208.5km route from Maubourguet Pays du Val d’Adour to Bergerac and is expected to suit the sprinters. The podium contenders will have a last chance to gain time in tomorrow’s time trial, prior to Sunday’s ceremonial sprinters’ stage on the Champs-Elysees.
A 20-rider breakaway dissolved on the ascent of yesterday’s third categorised climb, the fabled 17.1km Col du Tourmalet, with Mikel Nieve (Sky) and Blel Kadri (AG2R La Mondiale) pushing to the summit. Valverde attacked on the descent of the Tourmalet. Nieve attacked on his own on the lower slopes of the 13.6km finishing ascent of Hautacam. Chris Horner (Lampre-Merida) attacked and Nibali went with him, before dropping the American. The Italian then passed Nieve before going alone, demonstrating he is the supreme rider in the race and on course to become the sixth rider to win all three Grand Tours of France, Italy and Spain.