Golf-Koepka takes Byron Nelson lead, Spieth two back

* Koepka fires a 65 to move two ahead * Battling Spieth alone in second after a 67 (Adds detail, quotes) May 21 (Reuters) - Brooks Koepka was exasperated with his ball striking but made three birdies on the back nine to charge past hometown favourite Jordan Spieth and into a two-shot lead after the AT&T Byron Nelson third round in Texas on Saturday. Seeking a second PGA Tour win, Koepka posted a five-under-par 65 for a 16-under total at the TPC Four Seasons Resort in Irving, while fellow American Spieth closed with bogeys at 14 and 18 for a 67 to drop back into second place. "I putted well today and that's about all I can say," the 26-year-old Koepka told reporters. "That was about the worst ball-striking performance I've had as a professional. It was embarrassing after the first nine holes, but I kept it together. "It wasn't just off the tee -- it was wedges, irons, everything but the putter. I hope to get things straightened out for tomorrow. But I'm proud of the way I hung in there." Koepka and Spieth began the third round in a four-way tie for second with Spaniard Sergio Garcia and American Bud Cauley, one stroke behind overnight leader Ben Crane. Koepka, however, failed to make an early move as he traded two birdies with two bogeys and two pars in his first six holes. Spieth, meanwhile, was also frustrated with his play but he scrambled superbly and jumped out in front with four birdies in his first 11 holes. One stroke clear, the U.S. Open champion found water with an errant tee shot at the par-four 14th, resulting in his first bogey of the day and a two-shot swing there as Koepka drained a 20-foot birdie putt. "It was the same for me as the first two days, except even worse ball-striking and I putted better," said world number two Spieth. "Some of those up and downs were kind of ridiculous. It surprised even me and I practise those shots. I was in some tough spots. "It was a very stressful round of golf to play because I really don't have confidence with the ball right now. It was frustrating and actually pretty incredible to be in this tournament right now." Americans Matt Kuchar (65) and Cauley (68), and Spaniard Garcia (68), were tied for third at 13-under while American Crane struggled to a 72 to fall six strokes off the pace. (Reporting by Tim Wharnsby in Toronto; Editing by Mark Lamport-Stokes)