After a blistering opening round of 63, Woods was not at his best on day two at Lemont, Illinois.

But the world number one hung on to his slender advantage with eight pars on a tricky homeward nine to finish one clear of David Toms on 133.

"I just didn't quite keep it going," Woods said afterwards.

"I didn't drive it very good but the only good thing is I was really putting well."

WESTERN OPEN LEADERBOARD 133: Tiger Woods 134: David Toms 135: Cliff Kresge, Scott Verplank 136: Robert Allenby

Referring to Thursday's record-equalling round, the American said: "Some days golf can be, as we all know, one of the easiest games we've ever played, and then the very next day it's, like, 'is this the same person?'"

"I certainly didn't feel as good over the shots today like I did yesterday."

Cliff Kresge (68) and Scott Verplank (65) are tied for third spot on 135 while Australia's Robert Allenby (67) lies fifth on 136 after shooting a five-under 67.

Canada's Mike Weir, the US Masters champion, is a further stroke adrift along with US Open winner Jim Furyk.