'I wanted to shoot a 29 on one side, I wasn't real worried about being on the leaderboard,' said Blake, whose 6-under 64 at soggy Brown Deer Park left him one shot in front of Kirk Triplett.
Blake's luck started to turn when he birdied the par-5 18th, his ninth hole. It was one of six birdies in an eight-hole stretch.
'It's kind of nice to write 29 on your scorecard. You don't do that too often,' said Blake, whose only PGA Tour victory came 12 years ago at the 1991 Shearson Lehman Brothers Open.
Blake made a 40-foot birdie putt on the 485-yard, par-4 fourth, which used to be a par-5 until a large oak tree was removed this year.
Shigeki Maruyama, who won the GMO two years ago, was at 66 along with Jerry Kelly, Joel Edwards, Brett Quigley and Kenneth Staton.
Defending champion Jeff Sluman had a 72 on the 6,759-yard course.
Blake went out in the afternoon, when winds picked up and the weather was cool. The five golfers who shot 66s went out in the morning following overnight rains.
Kelly almost joined Triplett in second place with a 65, nearly chipping in on his final hole, the par-4 ninth. The ball hit the pin, bounced into the hole and back out.
'I thought that was in from the second I hit it,' Kelly said. 'It was in. It just didn't say in.'
Kelly thought more golfers would surpass his 66 in the afternoon.
'It was a pretty tough morning. It was so misty and rainy,' said Kelly, who had to switch clubs because the ball wasn't carrying well.
The afternoon brought tricky winds and overcast skies, however.
'It was pretty windy today, difficult to judge the conditions,' Triplett said. 'A little wet, a little cool. The ball's not going as far, I don't think, as you're used to. But the greens are soft and of course in great shape.'
The par-70 course with notoriously thick rough measures 6,759 yards, one of the shortest on the PGA Tour, so it puts a premium on iron play and putting while neutralizing long hitters.
With rains pummeling the course for several days, several golfers said the rough is of U.S. Open quality.
'It's probably not as consistent. It's certainly longer than the U.S. Open,' Triplett said. 'And they haven't topped it off. I think we usually top off at four and a half inches and it's seven, eight, 10 inches long in places, even right off the edge of some of the greens.
'And it's laying down and matted down in a lot of spots. It was very, very nasty, just a real guessing game.'
Divots: Brian Bateman withdrew after nine holes with an injured left knee. ... Sluman has missed the cut in his last three tournaments. ... Steve Pate had to putt with his driver after breaking his putter on his eighth hole. ... Asked if he regretted not coming to Milwaukee earlier in his career, Triplett said: 'Yeah. I wish I'd have found that Kopp's custard place a few years earlier.' ... Skip Kendall's 3-over 73 marked just the second time in 25 rounds at the GMO since 1997 that he's failed to shoot par or better at his hometown course.
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