Sweden\'s Robert Karlsson fired a five-under par 65 to take a three-shot lead at the halfway stage of the USPGA Tour St. Jude Classic. Karlsson, who started the day a stroke off the lead of David Mathis, had six birdies and one bogey en route to a 36-hole total of nine-under 131. Colt Knost and Keegan Bradley were tied for second on 134. Knost carded a 68 and Bradley a 67. Bradley, who won the Byron Nelson Championship a fortnight ago, is among the few players here this week who can earn a spot in the upcoming US Open championship at Congressional by capturing a second US tour title since the previous US Open. Karlsson, an 11-time winner on the European tour, lost here a year ago in a three-way playoff won by England\'s Lee Westwood. Rather than leaving a sour taste, Karlsson said that playoff appearance was a help as he tackles the TPC Southwind course again. \"It\'s actually a bonus that I did well here last year,\" he said. \"But this year is a new year, and even now most likely going to be in the lead after two days makes no difference. \"We\'ve come halfway, and who knows. I might finish 55th. You never know. You\'ve got to keep going, especially on punishing golf courses like this.\" Karlsson started his round at the 10th tee and birdied his second hole, the par-three 11th, where he hit an eight-iron to eight feet. After par saves at 12-14, he nabbed back-to-back birdies at 15 and 16 and again at 18 and one. At the par-four 15th he hit a wedge from 106 yards to seven feet to set up his birdie. Karlsson was in the rough off the tee on 16, but recovered with a wedge to five feet. He left himself four-footers for birdie at 18 and one. His last birdie of the day was a 14-footer at the par-four sixth, before he gave a shot back with a three-putt at the par-three eighth. \"I hit a bunch of good iron shots. It was nice obviously to get it going. As you said, it\'s not an easy golf course,\" Karlsson said. \"You just don\'t walk out there and shoot 68, 67. It\'s always nice to get off to a good start.\" Bradley, who missed the cut at Memorial last week after his Byron Nelson victory, said he thought he was back on track. \"Never had to do all the media that I had to do. Obligations that a winner has to go through, which I\'m so happy I had to go through it, but it took me a little bit by surprise,\" he said. \"But I feel good and feel rested now.\"