Keegan Bradley followed up his 10-under par first round with a one-under 69 to maintain a three-stroke lead in the Byron Nelson golf championship in Irving, Texas.
The former PGA Championship winner couldn't match his opening-round exploits, but had four birdies against three bogeys on a windy afternoon on the par-70 course to stay on top of the leaderboard with an 11-under par total of 129.
Despite the more difficult conditions, the American emerged with the lowest 36-hole total at the tournament since 2001.
Bradley, whose 2011 victory in this event was his first on the US PGA Tour, got off to a rocky start when he missed the fairway at the first en route to a bogey.
At the 18th he drove into the right rough under the trees and eventually missed a putt to save par.
Tom Gillis took advantage of the more benign morning conditions to shoot seven-under 63 for a share of second place on 132 alongside South Korea's Bae Sang-Moon.
Bae, who has won 11 times worldwide but has never on the US PGA Tour, carded his second straight 66, his round featuring six birdies and two bogeys.
It was a further stroke back to John Huh (64), Ryan Palmer (68) and South African Charl Schwartzel (70) on 133.
"It was a bit up and down out there," said former Masters champion Schwartzel, who had three birdies and three bogeys.
"Bit of a frustrating day, but I suppose it's the mix."
Argentina's Angel Cabrera carded a 69 to head a group of six players on 134.
Chinese schoolboy Guan Tianlang, who last month became the youngest golfer in Masters history, stumbled to a second-round 77 that left him on 147, well outside the cut line of even par 140.
The 14-year-old Asian prodigy won the Silver Cup as the low amateur at the Masters after finishing 58th at challenging Augusta National, and also made the cut last month in New Orleans, where he finished 71st.
"I won't make the cut every time. But I think I learned more," he said. "Just didn't play my best out there today. I still learned a lot. Still have a lot more to learn."
Of the Aussie contingent, Nathan Green was best placed, hitting four birdies on his way to a two-under 68 round to sit six shots off the pace while Marc Leishman and Cameron Percy were a further shot back.
Stuart Appleby fired an even-par 70 round to finish with a total of 139 at the halfway point while Jason Day, sitting a further shot back, rocketed 52 places up the leaderboard after carding 68.
In Mobile, Alabama, Jessica Korda shot a 7-under 65 to take a one-stroke lead over Australian Karrie Webb after the second round of the Mobile Bay LPGA Classic.
Korda had seven birdies in her second straight bogey-free round to reach 13-under at the Robert Trent Jones Golf Trail's Magnolia Grove complex.
"I'm hitting the ball good and I'm having a lot of fun, " Korda said.
"I feel really comfortable out here. This is definitely one of the stops I wanted to come back to and I hope we can keep this event as long as possible because I really like it."
The daughter of former tennis player Petr Korda, the 20-year-old won the 2012 Women's Australian Open for her lone LPGA Tour title.
"Really the tournament starts on the back nine on Sunday," Korda said. "So right now, it's great to have the lead and I feel good."
Seven-time major winner Webb also had a bogey-free round, birdieing the last three holes for a 63.
The 38-year-old Webb won the last of her 38 LPGA Tour titles in 2011.
Chella Choi was two strokes back at 11-under after a 66.
Sydnee Michaels had a course-record 62 to join Pornanong Phatlum (65) and Thidapa Suwannapura (67) at 10-under.
Defending champion Stacy Lewis was four-under after a second straight 70. She had a double bogey in the par-3 14th after finding the water. Michelle Wie missed the cut with rounds of 74 and 75. Brittany Lincicome also missed the cut, shooting 75-70.