Toyota's Sebastien Ogier was third with his world rally title rival Elfyn Evans poised just five seconds off the pace after Friday's breakneck racing at a frozen and foggy Monza.
Welsh driver Evans leads his Toyota teammate by 14 points in the season standings and only needs to finish fourth or better to deny Ogier a seventh world crown.
After six of the 15 specials the rally itself was being led by Dani Sordo of Hyundai followed by Esapekka Lappi of Ford.
With Northern Italy hit by snowstorms and chilly weather earlier in the week the tension was cranked up as the pair tracked each-other closely.
"It was tough, we were sliding all over the place out there and there was just no room for mistakes," Ogier said after Friday's sixth special.
Thierry Neuville of Hyundai was second overnight but crashed out after spinning in a huge puddle next a giant mound of gravel.
With the constructors title also up for grabs for the Belgian did everything he could but had to pull out as he engine overheated.
On Saturday, soaking conditions are expected to continue with six further specials at the specially adapted Monza race circuit that also hosted the world cycling championships.
The 31-year-old Evans is hoping to become the third Briton to win a World Rally title after Colin McRae and Richard Burns.
Evans won in the snow in Sweden and on the sizzling dirt tracks of Turkey in his first season at Toyota since leaving Ford.