Woods stands at 11-under-par 133 and owns a one-shot lead over last week's St. Jude Classic winner, David Toms. The 2001 PGA Champion carded a 3-under 69 in the second round.
Cliff Kresge (68) and Scott Verplank (65) are tied for third place at 9-under-par 135.
Woods matched the Cog Hill course record Thursday with a 9-under 63 and wasted little time in breaking into red figures Friday. He knocked an 8-iron to a foot for a birdie at the first and added a 15-footer for birdie at the third.
Woods reached the green in two with a 4-iron at the par-5 fifth and two-putted from 30 feet for his third birdie in five holes.
'I got off to a perfect start,' said Woods, a two-time former champion of the Western Open. 'I just didn't quite keep it going.'
Woods found trouble at the seventh when his drive found the hazard on the right side. He took a drop, then hit his third into the lip of bunker. Woods did well enough to make bogey at the hole and added a birdie at the par-5 ninth when his second found the greenside bunker and he blasted out to two feet.
He hit an enormous drive at the 13th, but hooked a 9-iron into a bunker on the opposite side of the pin. Woods pitched out to three feet, but blocked the putt and left with his second bogey of the round.
Woods played even-par the rest of the way and that included a great save at the par-4 closing hole. His drive found the lip of a bunker and all he could manage was a blast out into the fairway. Woods wedged his third shot to 10 feet and sank a 'beautiful' breaking putt to save par and polish off his round of 70.
'I certainly didn't feel as good over the shots today like I did yesterday,' said Woods, who has not won on tour since Bay Hill in March. 'A couple times the wind crept in there and gave me a little indecision and consequently I made a poor swing, and that's the hard thing about golf. You've got to go out there and hit good quality shots, and I didn't do that today.'
Toms, who opened with a 65 on Thursday, started on the 10th hole Friday and birdied the 12th after hitting a 6-iron to 10 feet. At the par-5 15th, Toms used a lob-wedge for his third shot and stopped the ball 12 feet from the cup, where he sank the birdie putt to get 9-under for the championship.
Things got worse for Toms, who also won the Wachovia Championship in addition to last week's triumph in Memphis. He missed the fairway at 16 and consequently missed the green. He bogeyed that hole and lost another stroke to par at 17 when he landed in a horrible spot off the tee.
Toms rebounded on his second nine. At the first, he hit a pitching-wedge to six feet and converted the birdie putt. Four holes later, Toms had to punch out from a difficult lie, but hit his third at the par-5 hole to 12 feet to set up birdie.
Toms reached the green in two at the par-5 ninth and two-putted for birdie to get within one shot of Woods' lead.
Woods and Toms met in the final of the WGC-Accenture Match Play Championship. Woods came out on top that day, but Toms put up a good fight while battling food poisoning earlier in the week.
'I look forward to tomorrow,' said Toms. 'He's obviously playing well right now and rounding into form, and I'm playing good, too, so maybe we can feed off each other and have a good day tomorrow.'
Robert Allenby is alone in fifth place at 8-under par, followed by Masters champion Mike Weir (70), U.S. Open winner Jim Furyk (66), Robert Damron (69), Heath Slocum (70) and Jason Gore (70). That group is tied for sixth place at 7-under-par 137.
The 36-hole cut fell at 1-under-par 143 and among those who missed the cut were: Jeff Sluman (144), Stuart Appleby (147), Jeff Maggert (149), Brad Faxon (150) and Ty Tryon (155).