By Steve Keating

AUSTIN, Texas (Reuters) - Red Bull's championship leader Sebastian Vettel continued to set a blistering pace at the U.S. Grand Prix, clocking the fastest time in final practice on Saturday.

Vettel, fastest in Friday's two practice sessions, has quickly mastered Formula's newest venue, the Circuit of the Americas, turning in a best time of one minute 36.490 seconds on a chilly but sun-bathed morning in south Texas.

McLaren's Lewis Hamilton, winner of the last U.S. Grand Prix in Indianapolis five years ago, was second-fastest crossing 0.258 seconds behind the German with Venezuelan Pastor Maldonado third in his Williams 0.511 off Vettel's torrid pace.

Ferrari's Fernando Alonso, the only driver left with a chance of preventing Vettel from clinching a third straight drivers' title, had an rough morning but produced a flying late lap to jump up the timing table into fourth 0.690 behind his German rival.

With the hour session drawing to a close, Spaniard Alonso had looked ready to improve on his position until he slid wide in the final turn entering the home stretch spoiling the attempt.

Vettel, who started the last race in Abu Dhabi from pit lane as punishment for a fuel irregularity, will be bidding for his sixth pole of the season later on Saturday as he tries to fend off a challenge from Alonso and collect a third straight drivers crown.

(Editing by Gene Cherry)