By Alan Baldwin
AUSTIN Texas (Reuters) - Championship leader Lewis Hamilton laid down a marker on Friday after leading title rival team mate Nico Rosberg in a familiar Mercedes one-two in first practice for the U.S. Formula One Grand Prix.
The Briton, chasing his fifth win in a row and 10th of the season, lapped with a best time of one minute 39.941 seconds on a gusty but bright morning at the undulating Circuit of the Americas.
Rosberg was 0.292 seconds slower than the 2008 world champion with McLaren's Jenson Button third fastest in a session of just 18 cars after Caterham and Marussia went into administration and failed to make the journey.
Hamilton leads Rosberg by 17 points with 100 still to be won, thanks to double points in the Abu Dhabi finale, in the three races remaining.
Mercedes, who have already wrapped up the constructors' title, can equal McLaren's 1988 record -- set by Alain Prost and the late Ayrton Senna -- of 10 one-two finishes in a season in Sunday's race.
There were only 16 races back in those days, however, compared to the current 19.
Toro Rosso's Russian rookie Daniil Kvyat, who graduates to the main Red Bull team next year in place of departing four times champion Sebastian Vettel, was fourth fastest ahead of Denmark's Kevin Magnussen in the other McLaren.
Vettel is set to start Sunday's race from the pitlane after exceeding his allocation of power units, and the talk before the race was that he would skip Saturday's qualifying to save the engine.
However Red Bull principal Christian Horner assured the fans that the German, who was seventh fastest on Friday morning, would be appearing.
"We'll certainly be taking part in qualifying," he told the BBC. "But we have to be very careful with our mileage, he has to get through three race weekends with this unit."
Ferrari's Fernando Alonso, still keeping everyone guessing about his future plans, was sixth fastest.
Red Bull's Australian Daniel Ricciardo, the only man other than the Mercedes drivers to have won this season, suffered a power unit problem that limited his track time and left him 17th.
Williams' Brazilian reserve Felipe Nasr completed 19 laps in the car Valtteri Bottas will race on Sunday and was eighth fastest while Toro Rosso gave Dutch teenager Max Verstappen a another session ahead of his race debut next year.
Verstappen was 10th fastest.
The session ended with drivers trialling a new 'virtual safety car' system, being tested as a means of reducing speeds electronically across the field when yellow flags are waved without introducing the real vehicle.
The system is being looked at following Frenchman Jules Bianchi's horrific Japanese Grand Prix accident. The Marussia driver remains critical in hospital a month on.
(Reporting by Alan Baldwin, editing by Toby Davis)