Six times world champion Sebastien Ogier and Belgian rival Thierry Neuville were separated by just 4.3 seconds after the penultimate leg of the season-opening Monte Carlo Rally on Saturday.
Ogier, returning to Citroen after winning his titles with Volkswagen and M-Sport Ford, is chasing a sixth successive victory on the icy roads of the French Alps.
Hyundai's Neuville, overall championship runner-up last season, has a mere four stages and 64km of competitive action on Sunday in which to deny the Frenchman another win on home asphalt.
Ogier, who grew up in nearby Gap and had started the day with a two-second advantage, joked that he had at least managed to double his lead over the penultimate leg.
"Once again today we had to find the right balance between pushing when it was dry and being cautious where it was icy and more slippery," said Ogier.
"I'm expecting the final leg to be really close, but perhaps the conditions won't be so tricky."
Neuville recognised it would be a big challenge to overhaul the local favourite but he would do his best.
"The game is still very much on," he said. "We have lost 2.3 seconds compared to Ogier over four stages, which is not too bad.
"I know I could have gone faster in some places, especially this morning, but if you push too much it's easy to make a mistake. I didn't want to take any risks but at the same time we had to keep the pressure on Ogier.
"It is his home rally so he knows the area very well. We will, of course, try to win tomorrow but we also have to be clever and think about the bigger picture."
France's nine times world champion Sebastien Loeb, returning with Hyundai for a limited season, was in third place and nearly two minutes behind the leaders.
Norwegian Andreas Mikkelsen, who had nurtured hopes of a top-three finish, retired from the rally after stage nine with a broken wheel after hitting a wall and wrecking the rear left side of his Hyundai.
Sunday's final stages include the famous Col de Turini, with five extra points also available to the winner of the closing Power Stage.