* Bradley remains three ahead after carding a 69
* American Gillis and Korean Bae tied for second
* Chinese teenager Guan misses the cut
Former champion Keegan Bradley maintained a three-shot lead in Friday's second round of the Byron Nelson Championship in Irving, Texas after grinding his way to a one-under-par 69 in increasingly tricky conditions.
Three ahead of the chasing pack overnight after opening with a blistering course record 60, Bradley had to contend with strengthening winds and firming greens at the TPC Four Seasons Resort Las Colinas en route to an 11-under total of 129.
American journeyman Tom Gillis (63) and South Korean Bae Sang-moon (66) were tied for second but China's 14-year-old Guan Tianlang made an early exit, missing his first PGA Tour cut in three career starts after battling to a 77.
A day after tying the tournament record of 60 held jointly by Sam Snead (1957) and Arron Oberholser (2006), Bradley mixed four birdies with three bogeys to preserve his place at the top of the leaderboard.
Though he dropped his final shot of the day at the par-four last where his tee shot sailed well right and he failed to get up and down from left of the green, he was delighted with his score.
"I'm really happy shooting 69," Bradley, winner here in 2011 before going on to claim his first major title at the PGA Championship just three months later, told reporters.
"I'm almost more proud of this round than yesterday because I didn't feel comfortable all day. I was a little uncomfortable and then I settled it and hit some really good shots."
Gillis, bidding for his first PGA Tour title after spending much of his golfing career competing on the lower tier circuits, was also in an upbeat mood after rocketing into contention.
"I'm pleased obviously," the 44-year-old said after a red-hot round tarnished slightly by a three-putt bogey on his final hole, the par-four ninth. "I made a bunch of putts.
"At the last I hit it pretty close, to about eight feet or nine feet so I was a little disappointed with that but overall it was good, really good.
"I just gave it a little too much speed," Gillis said of his first putt on the ninth green. "I probably lost concentration on the comebacker, so I guess that happens."
While Gillis was among several players in the morning wave who took advantage of calmer weather and preferred lies on a layout softened by rain earlier in the week, Chinese sensation Guan plummeted down the leaderboard.
Guan, who made his second consecutive PGA Tour cut at the Zurich Classic of New Orleans last month, followed his opening 70 with a 77 to finish well outside the cutline of level-par 140.
Competing this week on a sponsor's exemption, Guan carded five bogeys, two birdies and two double-bogeys, the last of them coming on his final hole, the ninth, where his tee shot ended up in water.
"I won't make the cut every time, but I think I learned more," Guan said.
The Chinese teenager has been one of the biggest talking points in golf since he became the youngest player to make the cut in a major championship at the Masters five weeks ago.
Also failing to advance were former major winners Yang Yong-eun of South Korea, South African Trevor Immelman and Americans Ben Curtis and Lee Janzen.