World Rally Championship form driver Ott Tanak set the benchmark time during Thursday's Rally Argentina shakedown stage.
The Estonian's time of 2min34.9sec was set on his first run of the 2.64-mile stage, and was not bettered by either the Toyota Yaris driver nor any of his rivals.
Following behind was points leader Thierry Neuville in his Hyundai i20 and Tanak's team-mate Kris Meeke.
Both were seven tenths of a second down, while defending world champion - and a driver seeking his first win in Argentina - Sebastien Ogier was 1.2 seconds off.
All four of those drivers set their quickest times at their first attempt, with conditions deteriorating quickly afterwards.
"The road was getting worse all the time," said Tanak.
"It will be the same tomorrow.
"For the first time, the stage was OK, the grip was not so bad - just some mud in places.
"After that, we had to just make sure we didn't damage the car.
"Tomorrow [Friday] is going to be a tough day.
"The surface is already quite soft with the sand in some places and then with the mud as well - and we have some watersplashes, which will be really full with the rain. It's going to be interesting."
Teemu Suninen was top M-Sport runner in fifth place, as Hyundai's returning Norwegian Andreas Mikkelsen was equal eighth fastest with Jari-Matti Latvala, who celebrates starting his 200th WRC round this week.
The rally proper gets underway with a run through the Villa Carlos Paz streets on Thursday evening, before the first full day of competition on Friday.