Dani Sordo mastered treacherous conditions to lead Rally Spain and set up hopes of a home victory for the first time in 21 years.
Torrential rain turned gravel tracks in the hills above the Costa Daurada into a mudbath, with aquaplaning a constant threat in water-filled ruts. But Sordo's storming afternoon performance earned the Hyundai i20 pilot a 17.0sec lead over Sébastien Ogier.
New Zealanders Hayden Paddon and John Kennard hold a very close fifth position after an anti-lag system issue on their New Generation i20 World Rally Car.
Starting the day's predominantly gravel stages 10th overall following the previouos evening's rain-soaked super special stage in Barcelona, they quickly leaped up the leader-board to third overall with a second quickest time through the day's opening 12.50km stage. Paddon and Kennard pushed on as best they could, but with the day's schedule including only a tyre regroup, not a full midday service, they had to contend with the technical issues all day. There was action aplenty around them with the rally lead moving from Ott Tanak, to Hyundai's Thierry Neuville, to Ogier to Hyundai's Sordo by day's end.
"A difficult day, unfortunately," Paddon said.
"Near the end of the first stage we struck a technical problem we've had to carry for the rest of the day. Basically it's meant we're down on power with no throttle response. We've tried to manage it the best we can, but with no service it means we've had the problem all day. To be in P5 is probably still lucky, but it's very frustrating because it could have been very good. The car's been feeling good, even though the conditions have been quite tough.
"Never mind, we're still here with two days to go on the tarmac. We'll have to try and use this determination to try and claw some time back. Disappointing, it's not what we wanted and just need a bit of luck on our side."
The Kiwis are just 1.2 seconds away from fourth-placed Neuville prior to tackling two days of tarmac stages the next two days.
Championship leader Ogier, bidding to seal a fourth consecutive world title here, and Neuville each led during the morning's three speed tests. Sordo was sublime when they were repeated, winning two and placing second in the other to climb from fourth to first.
"This is a dream for me," said Sordo, hoping to become the first Spaniard to win on home ground since Carlos Sainz in 1995. "I have to say thanks to the team for a great job with the car. Tomorrow we need to continue and see what we can do. Two long days to go, but today was unbelievable."
Ogier endured the worst of the slimy roads from first in the start order and the Frenchman admitted his priority in the early afternoon stages was simply surviving in his Volkswagen Polo R.
Team-mate Andreas Mikkelsen completed the podium places, 18.1sec behind Ogier. The Norwegian overcame brake problems late in the day and twice slowed on stages when mistakenly believing he had a puncture.