(CNN) -- Tiger Woods shot a four-under-par 67 to share the lead with fellow American Mark Wilson at the halfway stage of the BMW Championship in Illinois on Friday.
Tiger Woods is joint leader with Mark Wilson at the BMW Championship in Illinois after a second round 67.
Wilson had been in front for most of the day after his second-round 66 put him on seven-under 135 and lifted him to the top of the leaderboard before world No. 1 Woods began his charge.
Woods had made an inauspicious start to the day when he bogeyed the first after he hooked his drive into fairway bunker, but it proved to be his only blemish as he quickly found form to hit five birdies, including one at the 17th which pulled him level with compatriot Wilson.
The American, who is a four-time winner at the Cog Hill course, admitted he had to remain patient on the demanding greens.
"I started off with a bogey there at the first hole, but other than that I didn't make any other bogeys. I had a few opportunities to make bogeys, but I had some good saves there at three and a few other holes," Woods told the PGA Tour Web site.
"It was a day where the wind was blowing just hard enough. It was kind of up and down, kept changing directions a little bit. These greens you have to be so precise going into them. We had some pretty tough putts today up over knobs, but also I hit a few in there pretty tight, too.
"As I said, I just had to be very patient out there -- there are a lot of holes to be played, and this is the kind of golf course you can just make a couple mistakes here and make a couple bogeys, or hit good shots and make bogeys. These greens are very difficult."
Ireland's Padraig Harrington missed the chance to join Woods and Wilson at the top after he bogeyed the 18th hole following a poor tee shot to card a 68 for the second consecutive day.
Overnight leader Rory Sabbatini of South Africa, Australia's Marc Leishman and American Bo Van Pelt were also at six under with Harrington after 36 holes.
John Rollins and Zach Johnson were the biggest climbers on the second day, both carding 65s to move on to four-under 138 alongside fellow Americans Brandt Snedeker, Sean O'Hair and Anthony Kim.
The $7.5 million tournament is the third event in the US PGA Tour's FedEx Cup playoff series.
A total of 70 players qualified for the penultimate playoff event, and the top 30 advance to the Tour Championship with a $10 million bonus for the winner on the line.
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