Dani Sordo holds the overnight lead after the first full day of Rally Monza, with both Sebastien Ogier and Elfyn Evans in title contention in the World Rally Championship decider.
The Spaniard won the opening stage of the morning but then M-Sport Ford's Esapekka Lappi gambled and put on one of the two sets of snow tyres which were allocated to each car for this event.
Behind the front two, title fighter Ogier holds third place 12s off Lappi, with points leader and team-mate Evans in fourth place 5.1s back but with a slender six-tenths gap on Hyundai's Ott Tanak.
Lappi's Fiesta WRC was considerably more sure-footed as a result, hoisting the Finn to the top of the order as the rest of the field struggled to find grip.
The routes laid out around the home of the Formula 1 Italian Grand Prix offered a combination of wet, muddy asphalt and waterlogged gravel beneath persistent driving rain, which challenged even the most experienced crews in the field.
A day of high anxiety for all the teams ended disastrously for Hyundai's Thierry Neuville. The Belgian arrived with a slender chance of overhauling the Toyotas of Ogier and Evans in the drivers' title race, but dropped 20 seconds on the opening stage of the day after spinning and stalling.
Although back on the pace after the second stage, Neuville then clouted a chicane with the right front corner and, in his eagerness to get to the finish, drowned the car in a water splash.
This effectively means that the drivers' championship battle is a two-way fight between the Toyotas of Evans and Ogier, with Hyundai's Tanak so far back that he needs both of them to fail to finish the rally, while claiming victory and maximum Power Stage points for himself, in order to retain his 2019 drivers' world crown.
Hyundai is therefore set to marshal its forces to try and secure the manufacturers' crown, holding a slender seven-point advantage over Toyota at the start of the event.
To that end, Sordo was able to push hard on the final stage of the day in order to take the overnight lead by one second from Lappi. The Spaniard will now enjoy the optimum road position of running last for the rest of the rally.
"Today was a really tough day," said Sordo. "We started quite good, after that we lost a little bit of time in the very muddy places because we didn't like it a lot - it was very, very tricky.
"At the end of the day I really tried to push for being in front, I think it's very important to be in the back (of the running order) and to have a little bit more clean lines."
In the private battle between the Toyota drivers, Ogier spun on the first stage of the day while Evans stalled. The Welshman won two of the day's stages and the pair went into the overnight halt with Ogier third and Evans fourth.
"It's really exactly the same as I expected, very stressful and challenging for the drivers I would say," Tommi Makinen, Toyota team boss, said. "I would say everybody might be a little bit nervous."
After witnessing Lappi's advantage on snow tyres, all teams bolted the more extreme rubber on for the afternoon session. As a result of this unexpectedly high demand, the FIA announced that two more snow tyres would be allocated to each car for the weekend.
Saturday sees the field leave the Villa Reale in Monza for two loops of three stages in the Bergamasque Alps, which have seen a deep covering of slushy snow build up in recent days. There is a small chance of more snow overnight but it is more likely to turn to slush under the winter rain, putting a premium on having the most robust tyres possible.
"I think we've all utilised the winter tyre today because of the extreme conditions," said Evans. "I think it's welcome for everybody that we have a couple of extra tyres.
"With the conditions as extreme as they are at the moment ideally we would need some studs but we don't have them and therefore we have to manage with the snow tyre."