Sebastien Ogier leads Citroen team-mate Sebastien Loeb by 1.6 seconds after SS8 in Mexico, meaning the younger Frenchman will have to run first on the road on Saturday.
The two works Citroens have battled for the lead throughout the opening day, with Loeb briefly nosing ahead prior to the mid-day service, before Ogier regained the lead on SS6. But he was never able to pull far away, and Loeb appeared to be driving carefully to ensure he slotted in behind his teammate at the end of the day's final full-length stage El Cubliete, which is when the running order for leg two is set.
Asked earlier in the loop if he was considering slowing tactically to avoid running first, Ogier said his plan was just to "continue to drive fast – I have no choice."
Running behind Ogier on the road today, Loeb was able to judge his teammate's pace and play a strategic game.
"Second on the road and I took one second back from Seb on that one," he said after SS8. "I tried to be as smooth as possible. So it's been a perfect day. It's still far to the finish because Seb is very, very fast. We have to push to the limit all the time to beat his times, so it will be a long, long rally."
Ogier could yet lose first place if the stewards decide to penalize – or even exclude – him for accidentally driving into service before going to the regroup at today's lunchtime halt. Though Ogier quickly realized his mistake and drove to the regroup instead, the officials have the option to penalise him for an incorrect route.
Pending a decision on Ogier, the two factory Citroens have the lead battle to themselves after Petter Solberg's huge delay on the Alfaro stage. The Norwegian discovered an electrical issue that had caused his dramatic loss of power and is now back up to speed - but is 7m34.9s behind the leaders in 13th place.
Ford's Mikko Hirvonen is not able to keep up with Ogier and Loeb either, and while he still holds third, he is now 1m19.6s adrift.
Matthew Wilson briefly got up to fourth place, potentially equaling his career best, only for his Stobart Ford to come to a halt with an apparent mechanical problem on Ortega.
After his morning puncture, Jari-Matti Latvala benefited from Wilson and Solberg's problems plus his own speed to vault from ninth to fourth in three stages this afternoon, ending SS8 just ahead of Stobart Ford's impressive and very happy returnee Evgeny Novikov.
"I'm very happy, it's a really good day," said Novikov, who has a 17s cushion over team-mate Henning Solberg. "We had a lot of fun today. The first section I just took care of it and I didn't push. On the second section I tried to push. Let's see what will happen tomorrow."
Ken Block's miserable rally continued when his Monster Ford stopped early on El Cubliete, taking him out of 15th place.
The cars are now returning to Guanajuato to end the leg with two more runs around the street-based superspecial.
Leading positions after SS8:
Pos Driver Team/Car Time/Gap
1. Sebastien Ogier Citroen 1h24m04.2s
2. Sebastien Loeb Citroen + 1.6s
3. Mikko Hirvonen Ford + 1m19.6s
4. Jari-Matti Latvala Ford + 2m51.3s
5. Evgeny Novikov Stobart Ford + 2m54.3s
6. Henning Solberg Stobart Ford + 3m11.7s
7. Dennis Kuipers Ferm Ford + 4m55.9s
8. Nasser Al-Attiyah Barwa Ford + 5m01.5s
9. Ott Tanak MM Ford + 5m25.7s
10. Martin Prokop Czech Ford + 5m52.1s