DANIEL Ricciardo set the pace as title rivals Lewis Hamilton and Sebastian Vettel suffered problems in Practice Two for the Mexican GP.
Ricciardo lowered the lap record set by Valtteri Bottas in Practice One to top the timesheet with a 1:17.801.
Hamilton was a tenth off the Australian in second - the championship leader recovering from a big spin on his first timed lap of the session - with Max Verstappen a further three hundredths of a second back.
Vettel was fourth but suffered a bizarre problem when the fire extinguisher in his car exploded. His Qualifying simulation was also compromised by an error on his first lap where he went wide at Turn 11, so the true pace of his Ferrari has yet to be truly revealed.
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Kimi Raikkonen and Valtteri Bottas completed the top six, both less than half a second off Ricciardo to suggest there could be a three-way battle for pole on Saturday.
Fernando Alonso was a very encouraging seventh for McLaren and just seven tenths down on the best time, although he will start from the back row after a 20-place grid penalty.
Meanwhile, Romain Grosjean and Pierre Gasly will enter Saturday with almost no running under their belts having sat out Practice One and suffered issues early in the afternoon session.
Grosjean span on his second lap and the resulting puncture caused terminal damage to his Haas and brought out an early red flag.
Gasly, meanwhile, was limited to just 10 laps by a power unit issue. Verstappen’s session was also brought to a premature close by an engine problem, although Red Bull team principal Christian Horner confirmed to Sky F1 it was not his race power unit.
Hamilton is guaranteed to win his fourth world championship on Sunday provided he finishes in the top five, while Vettel must outscore him by 17 points to take the title race to Brazil.
But the Briton’s race strategy may be compromised after his uncharacteristic mistake on his first timed lap on the supersoft tyre.
Hamilton lost his car through the exit of Turn 11 and was fortunate to keep it out of the wall but the lack of running on the supersoft will have left Mercedes with a lack of data.
“This doesn’t give the Mercedes the ideal scenario,” said Sky F1’s Paul Di Resta.
“They can’t put all the information into the computers and dictate what the best strategy is. They don’t know what that supersoft is going to do.”
Vettel, meanwhile, made a belated start to the session as Ferrari finished making set-up changes to his car.
The German was then forced into an early return to the pits and a change of overalls after his extinguisher leaked under his seat.
And on his opening flying lap on the ultrasofts, Vettel went off at the same place as Hamilton before ending up 0.250 seconds off Ricciardo.
Valtteri Bottas outpaced Lewis Hamilton in a Mercedes one-two in Practice One at the Mexican GP, on a weekend where the Englishman stands on the brink of winning his fourth world title.
Hamilton has dominated his Mercedes team-mate since the summer break but Bottas was the quicker of the two by a large 0.466-second margin in opening practice, after setting immediate lap-record pace on the ultrasoft tyres.
Red Bull and Ferrari, who are both expecting strong weekends, were over half a second off the pace but did not use the ultrasoft compound, the fastest available this weekend. Their respective cars lapped on the supersofts.
“We don’t know the delta between tyres yet but it looks like we have a race on our hands,” said Sky F1’s Martin Brundle.
Fresh from a belated apology to the US GP stewards on Thursday night, Max Verstappen was third ahead of team-mate Daniel Ricciardo although lost the final 20 minutes of the session after deciding to make a “big” set-up change to his Red Bull in time for Practice Two.
Sebastian Vettel, who must outscore Hamilton by 17 points on Sunday to keep the title fight alive to Brazil, was fifth amid a messy session in which he twice went off the circuit, once across the grass.
Local hero Sergio Perez, whose presence in the field is helping ensure a sell-out crowd for race day, was a promising seventh after pipping McLaren’s Fernando Alonso, although the Spaniard brings a 20-place grid penalty into the weekend.
But Force India’s Mexican tester Alfonso Celis, taking over Esteban Ocon’s car for P1, crashed into the Turn 16 barriers to bring out the red flags in the session’s final quarter of an hour.
On a dusty track surface, Ferrari’s Kimi Raikkonen (sixth fastest) spun as did Sean Gelael (17th) in the Toro Rosso on his latest P1 outing.
McLaren’s Stoffel Vandoorne completed just three laps after the new Honda power unit installed on his car for the session developed a problem and had to be changed.
The Belgian is already destined to start at the back of Sunday’s grid after collecting a 35-place penalty. In addition to Alonso’s 20-place demotion, Toro Rosso’s returning Pierre Gasly has a five-place penalty for new engine elements.