World champion Max Verstappen of Red Bull set the fastest time in Friday's practice for the Miami Grand Prix while Ferrari's Charles Leclerc suffered a crash into a barrier on a track which several drivers described as "slippery".
After Mercedes enjoyed a 1-2 effort in the opening session, with George Russell leading the way from Lewis Hamilton, Verstappen – the current championship leader – responded emphatically with an impressive best lap time of 1:27.930.
Ferrari's Carlos Sainz was 0.385 seconds behind closely followed by his teammate Leclerc, whose session ended early after he went nose first into the barrier at Turn eight.
Leclerc left the track on a moped and showed no signs of any side-effects from the incident, which caused a red flag and five-minute delay, frustrating teams who were putting in some longer runs.
Verstappen's second practice, on the newly resurfaced Miami track, was accompanied by regular complaints from the driver about his headrest but the discomfort appeared to have little impact on his performance.
"It was a good day. Initially we were getting used to the track with the new tarmac, it was ramping up a lot throughout the day. It's still quite slippery off line but on the driving line it's OK," he said.
"Most importantly today we had good balance in the car so I feel happy. There are still a few things we want to look at overnight, ideally we want to be faster on every corner, which isn't always possible. We'll have to see what the weather will do tomorrow, but overall it's been a positive day," he said.
The weather forecast for the weekend predicts rain but it is more likely to fall on Sunday rather than for Saturday's qualifying.
Verstappen's teammate Sergio Perez, who is just six points behind him in the standings after his win in Baku last week, was fourth fastest ahead of Aston Martin's Fernando Alonso.
Red Bull drivers have dominated the opening four races of the season with Verstappen and teammate Sergio Perez claiming two victories each.
The lack of over-taking in a largely processional Azerbaijan Grand Prix, combined with the Red Bull cars' superior speed, has led to fears of a season lacking drama and excitement.
After Russell posted a time of 1:30.125 in the earlier session, with his fellow Briton Hamilton second quickest, 0.212 behind, there was at least some indication that Red Bull might not have it all their own way on Sunday.
But even before the second session, Mercedes team principal Toto Wolff was quick to caution against reading too much into their times.
Hamilton finished seventh in the second session while Russell was down in 15th, 1.286 off Verstappen's pace.
"I'm going to stay optimistic and hopeful that we can get the car in a better place for (Saturday) and maybe be a couple of positions further forward," said Hamilton.
"We weren't particularly quick, and it was a struggle out there. The grip is quite low on this new surface. It is slippery, particularly for the rear-end. The track temperature today was very high so there was lots of sliding. (First practice) looked quite good but our pace in (the second practice) was a kick in the guts. We're trying lots of different things and we'll keep working on it," he said.
Last year's maiden Miami race was met with criticism from drivers about the grip on the track when moving out of the regular driving line and it appears that the newly laid tarmac still has some issues.
"So far, I think the new track surface seems to be better, but we were basically just cleaning the racing line today," said Alonso.
"It seems when you move away from it, it's very slippery – so that could make overtaking difficult," he added.
The first practice also saw a red flag after Haas' Nico Hulkenberg lost control of his car entering turn three, spinning into the wall and leaving debris on the track from his front end.