Bradley maintains Byron Nelson lead

Keegan Bradley followed up his stellar 10-under-par first round with a 1-under 69 on Saturday (AEST) to maintain a three-stroke lead in the US PGA Tour Byron Nelson Championship.

Former PGA Championship winner Bradley could not match his opening-round exploits, but he had four birdies against three bogeys on a windy afternoon on the par-70 TPC Four Seasons Resort course to stay atop the leaderboard with an 11-under total of 129.

Despite the more difficult conditions, Bradley emerged with the lowest 36-hole total at the tournament since 2001.

"I'm almost more proud of this round than yesterday because I didn't feel comfortable all day," said Bradley, who bookended his round with bogeys at the first and 18th.

"I don't know what it was, I can't put my finger on it but, you know, I bogeyed the first hole. I was a little uncomfortable and then I settled in and hit some really good shots."

Australia's Nathan Green moved up a place to a tie for 13th with a 2-under round to sit at 5-under overall, while compatriots Marc Leishmann and Cameron Percy are both tied for 21st at 4-under.

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 a seven-under 63 that gave him a share of second place on 132 alongside South Korea's Bae Sang-Moon.

Bae, who has won 11 times worldwide but has never won 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."