Mikko Hirvonen won the first four stages of Wales Rally GB as Ford team-mate Marcus Gronholm edged ahead of championship rival Sebastien Loeb.
Hirvonen has set the early pace in foggy conditions
Loeb, needing only a top-five finish to secure his fourth world title for Citroen, took no risks in slippery conditions in the South Wales forests.
The Frenchman finshed third on day one, 2.9 seconds adrift of Gronholm.
"I don't need to push to the maximum," said Gronholm. "We just need to wait and see what happens to Sebastien."
Finland's Hirvonen finished day one 25.6 seconds clear of his compatriot Gronholm, who is competing in his final rally before retirement.
Stobart Ford's Jari-Matti Latvala, another Finn, was running in fourth place with Subaru's Norwegian Petter Solberg pushing hard behind him.
Loeb leads Gronholm by six points in the standings and has won eight rallies this season to the Finn's five.
Ford have already made sure of their second successive manufacturers' title.
"It will be a bit stupid in my situation to take lots of risks to try and win here," said Loeb on Thursday.
"I've not started a rally in this position before - normally when I start I want to go as fast as possible and go for the victory."
In Friday's first leg the drivers complete six timed stages, including one in full darkness, totalling 140.8 km mostly through the forests of the Vale of Neath.
Two spectators were taken to hospital in Swansea with minor injuries after a privately-entered Subaru driven by Briton Simon Harraway went off the track in the opening stage.
The crew were unhurt but the stage was stopped after the incident.