By Steve Keating

AUSTIN, Texas (Reuters) - Red Bull's championship leader Sebastian Vettel will start the U.S. Grand Prix from pole position on Sunday with the German perfectly placed to secure his third Formula One title in succession.

Ferrari's Fernando Alonso, 10 points behind with two races remaining including Sunday's and the only man who can deny Vettel the title, set only the ninth quickest time in Saturday's qualifying.

The Spaniard will move up to eighth on the starting grid, and right behind Brazilian team mate Felipe Massa in sixth, due to a five place penalty imposed on Lotus's French driver Romain Grosjean for an unscheduled gearbox change.

Alonso, who will have no problems getting ahead of Massa, will however have to start on the 'dirty' side of the grid.

Vettel, who dominated all three practice sessions at the sport's newest venue, will have McLaren's Lewis Hamilton alongside on the front row.

The Briton, last winner of a U.S. Grand Prix at Indianapolis in 2007, was just a tenth of a second slower.

"It was a bit closer than I wanted, but fantastic to start on the front and on the clean side," said Vettel, 25, of his sixth pole of the season and 36th of his career.

Red Bull are set to clinch the constructors' title for the third year in a row on Sunday and have Australian Mark Webber, Vettel's team mate, in third place on the grid with Finland's Kimi Raikkonen fourth for Lotus.

(Reporting by Steve Keating, editing by Alan Baldwin)