A victory by Steve Stricker last week at the Deutsche Bank Championship moved him in front of Woods in the PGA Tour's four-tournament playoff system, but Woods would regain the lead with a win this week.
He finished 36 holes at the Cog Hill Golf & Country Club with a 7-under 135 total, tied for the top spot with Mark Wilson.
They had a one-shot lead over first-round co-leader Rory Sabbatini, Bo Van Pelt, Marc Leishman and Padraig Harrington.
There are 70 players left to contend for the FedEx Cup and its accompanying first prize of $10 million. Only 30 will move on to the Tour Championship in Atlanta, where the FedEx Cup will be awarded.
Woods tied for second place at the opening playoff event, but was never in contention last week.
"I'm playing well and I've got up-and-down a few times the last couple days, something I hadn't done," Woods said.
Wilson is 41st on the points list and needs to stay near the top this week if he is to earn a berth in the Tour Championship.
"I'm not going to look at it (the points list) because it just would be too distracting," Wilson said.
Stricker shot a 2-over 73 Friday and dropped into a tie for 51st. Phil Mickelson fired a 69 and was tied for 19th at 140.