Miami — Sergio Perez topped the times for Red Bull ahead of championship leader Charles Leclerc in Saturday's final free practice ahead of Sunday's inaugural Miami Grand Prix.
In hot, but changing conditions, the 32-year-old Mexican clocked a best lap in one minute and 30.304 seconds to outpace Ferrari's Leclerc by 0.194, with his Red Bull team-mate and defending world champion Max Verstappen third, three-tenths adrift.
Two-time champion Fernando Alonso, making light of his 40 years, was fourth-fastest for Alpine ahead of Sebastian Vettel of Aston Martin and Haas' Mick Schumacher, all of them seven-tenths off the leading pace.
Carlos Sainz was seventh for Ferrari ahead of Kevin Magnussen, Alex Albon of Williams and McLaren driver Lando Norris, but it was a disappointing day for Mercedes after their return to competitive form on Friday.
Seven-time world champion Lewis Hamilton was only 15th and George Russell, who was quickest in second practice, was 17th — with both appearing to struggle again with 'porpoising' in the closing stages of the session and with only two hours to resolve their problems before qualifying.
Verstappen was soon setting the pace, swapping quickest times with Leclerc, before Esteban Ocon crashed at Turn 14, prompting a red flag as his Alpine smacked the barriers.
The Frenchman came off at the same place where Carlos Sainz had hit the wall on Friday, a collision that curtailed his day for Ferrari and left him trying to make amends on Saturday.
After Ocon's incident, with 45 minutes to go, both Mercedes were once again in the top six — Russell in fourth and Hamilton sixth.
"We seem to be quicker, but I am not exactly sure why that is," Hamilton had explained. "We still have the bouncing, so we haven't cured it, but little by little we're improving the car."
Watched by former US First Lady Michelle Obama in the Mercedes garage, the Silver Arrows duo continued to enjoy the sunshine that, they said, played as much of a part in their resurgence as the car updates.
After a 15-minute break to clean up Ocon's car and debris, the action resumed.
"The race is going to be tough particularly as the tyres are over-heating," said Hamilton. "And it is very hot all day... I've already lost a few kilos! It reminds me of racing in Malaysia with the heat."
Of the track, Hamilton said it was "bumpy" but "nice to drive".
The challenging circuit was expected to create challenges and errors, particularly when a strong wind arrived with heavy-looking cloud cover. For Russell, it meant less grip and more 'porpoising' again.
"The tyres are nowhere," he reported as Perez and Verstappen took over at the top ahead of Leclerc, the top trio running a full second quicker than the rest with nine minutes remaining before a dramatic late escape for Verstappen who hit a kerb at Turn 13 and slid to a halt.