Padraig Harrington upstaged tournament host Tiger Woods with a course record nine-under-par 63 at the Target World Challenge.
The Irishman will now go into tomorrow's final round at Thousand Oaks in California six shots ahead of the world number one, who is also defending champion at this elite 16-player event.
Playing alongside Woods, Harrington eagled three of the par fives on the Sherwood Country Club course as he went on to card a 19-under-par total of 197.
Woods for once was the player in his pairing left in awe.
"Padraig played a beautiful round of golf," he said. "I've always said he's one of the best players in the world and he proved it today."
For the third consecutive day, Woods carded seven birdies, but his good work was wasted by five bogeys.
The American missed several short putts early in his round of 70, his worst of the week.
"It was a sloppy round of golf," Woods told www.tigerwoods.com. "I didn't play particularly well and it showed. I made a lot of mistakes.
"Tomorrow I just need to play a real solid front nine and eliminate my mistakes."
After Harrington, the next best score of the day came from European Ryder Cup team-mate Bernhard Langer, whose 67 left him one shot behind Woods on 12 under par.
Nick Price and David Toms are one stroke further back, while Colin Montgomerie and Jim Furyk are another shot adrift after both carded 68s.