Tiger Woods extended his sizeable lead at the Buick Invitational by shooting a six-under-par 66 in his third round at Torrey Pines near San Diego.

The defending champion's superb effort took him to an 18-under-par total of 198 and into an eight-stroke lead over Stewart Cink.

Cink shot a three-under 69 on the South Course to move to 10 under, with Joe Durant a further shot back on nine under after firing a 67.

Justin Leonard returned a seven-under 65 to share fourth spot with Doug Labelle (69), Aaron Baddeley (71) and Boo Weekley (71) on seven under.

Woods' eight-stroke lead after three rounds is the biggest in the tournament's history, surpassing the five-stroke advantages held by Gene Littler in 1954, Bob Goalby in 1967 and JC Snead in 1976. The world number one also tied the 54-hole tournament record, first set by Woody Blackburn in 1985.

Woods began his third round with a four-shot lead and went to the turn in two-under 34. He added four birdies on the back nine in a bogey-free round.

It was his 19th consecutive round in the 60s. The last time he shot in the 70s was in September in the first round of the Deutsche Bank Championship, where he finished tied for second.

He may already have enough with the final round in danger of being cancelled due to forecast heavy rains.