Lewis Hamilton set the pace in a rain-affected first practice session for this weekend's United States GP.
Although conditions improved through the session following heavy overnight rain in Texas, a damp and slippery track significantly reduced meaningful track running and meant all of the best times were recorded on intermediate tyres.
But befitting his reputation as a master of the rain, Hamilton was comfortably the quickest driver on show, setting the pace with a lap of 1:47.502 - a formidable 1.3 seconds ahead of Mercedes team-mate Valtteri Bottas in second.
Job done, Hamilton sat out the final 20 minutes of the session - a reflection, perhaps, not only of the conditions but his relaxed demeanour since arriving in Texas.
The Englishman only completed six laps, fewer than any other driver.
US GP Practice One results in full
The Mercedes driver will be crowned world champion for a fifth occasion if he out-scores Sebastian Vettel, his nearest title rival, by at least eight points in Sunday's race - underway at 7.10pm and live on Sky Sports.
Apparently struggling in an unbalanced Ferrari car, Vettel was only fifth quickest, behind the Red Bulls of Max Verstappen and Daniel Ricciardo.
Ferrari have introduced a new floor on their car this weekend as they seek to puncture Hamilton and Mercedes' recent momentum.
Sauber's Charles Leclerc briefly caused the session to be red-flagged after running wide and showering the track with gravel.
Both Sauber cars finished in the top ten, edging out the McLarens of Fernando Alonso and Lando Norris. Creditably, the British teenager was only two tenths behind Alonso.