Red Bull put Lewis Hamilton on notice, he will have work to do to grab another victory in Mexico.
Daniel Ricciardo put Red Bull on top of the second practice at the Mexican Grand Prix on Friday, edging defending race champion and season championship leader Hamilton by 0.131 seconds. Ricciardo's Red Bull teammate Max Verstappen was third.
Ricciardo has one victory and nine podium finishes this season. He had been on a strong run of three consecutive top-three finishes until that streak was broken with engine failure last week at the U.S. Grand Prix.
"I think these last three races will be pretty close between the top three teams," Ricciardo said.
Verstappen thought he had a third-place finish in Texas before he was penalized for an improper last-lap pass and was taken off the podium. Those two will look to challenge Hamilton for pole position on Saturday.
Ricciardo's fastest lap Friday was 1 minute, 17.801 seconds, a track record at the Autodromo Hermanos Rodriguez.
Hamilton is chasing a career fourth season championship and could get it Sunday by finishing no worse than fifth place. He has a 66-point lead over the Ferrari's Sebastian Vettel with three races left.
Vettel had an adventurous day, finishing fifth and fourth in the two practice sessions. His morning session included a drive into the grass at the end of the track's long straight into the first turn. In the second, his car's fire extinguisher leaked near the seat of his pants, forcing him into the garage for a suit change.
"Wasn't that pleasant for me," Vettel said. "It got very cold."
The portion of the track where Vettel ran into the grass has new curbs designed to force cars that run off to take a slow, winding return. Force India's Esteban Ocon said this week the curbs are so severe they could damage a chassis.
The design change came after two controversial decisions last year that helped propel Hamilton to a win and denied Verstappen a podium spot.
Hamilton flew into the grass at the start of the 2016 race and he rejoined the track in front of teammate Nico Rosberg. Race stewards determined Hamilton had a slight edge in position when he went into the grass, and therefore his return didn't change the drivers' position.
Verstappen made a nearly identical excursion off track near the end of the race, but his drew a penalty that spoiled would have been a third-place finish. Several drivers complained that Verstappen was penalized but Hamilton wasn't.
Verstappen came to Mexico trying to shake off last week's disappointment in Texas. Although he was defiant with reporters on Thursday, he later apologized on social media for harsh words over the race penalty.
"My comments were made in the heat of the moment, I know that the words I used were inappropriate and they were not directed at any one person. I certainly did not mean to cause any offence and I hope we can move on and enjoy this race weekend," Verstappen's Instagram post said.
Mercedes' Valtteri Bottas topped the first practice session but dropped to sixth in the second. Bottas has two wins this season but hasn't finished on the podium in the last three races.
