Volkswagen's Sebastien Ogier seemingly needs only to finish Rally Mexico on Sunday to wrap up a dominant victory.
The Frenchman opened up a lead of nearly three minutes over the field, helped by the retirement from second place of Ford's Mads Ostberg.
Mikko Hirvonen occupies second for Citroen with Thierry Neuville third for Ford.
Ostberg reported a clutch problem after stage 14 and a subsequent electrical issue with his alternator forced him out of the race.
"It's the biggest disappointment I've ever had in rallying," the Norwegian told wrc.com. "It's very frustrating after fighting for a good result.
"I can't believe it's the third rally in a row where we've had technical issues and I'm not happy with that. I hope this will change now."
Ogier responded: "Okay, It was a great morning for us but I feel a bit disappointed for Mads, he deserved better than that. This morning he did a really good job and it's a shame for him.
"Now we just want to get to the end, avoid all rocks and try to save the car as much as we can. We'll be very safe."
And he laughed off an incident on stage 18 in which he lost 30 seconds when he had to stop to open a gate.
"Maybe somebody didn't want me to win," he said. "We had to stop the car, get out and open it. Not perfect. Next time perhaps they should remove the gates."
The exit of the unfortunate Ostberg - who also suffered a foot injury when he kicked his car in frustration - allowed Neuville to climb to third despite losing almost a minute on stage 15, having damaged his steering when he hit a rock on the day's opening stage.
But the Belgian was handed a route back into contention when Hirvonen suffered a puncture on stage 18 at Otates.
Spain's Dani Sordo was fourth despite struggling in the morning, when he said: "I can't drive the car. I don't understand it.
"If I try to go faster then I will go out of the road. If I knew what the problem was, then I would change the car."
Nasser Al-Attiyah, Ken Block, Chris Atkinson, Benito Guerra, Martin Prokop and Evgeny Novikov round out the top 10.
