By Simon Evans NORTON, Massachusetts, Aug 30 (Reuters) - Tiger Woods appeared untroubled by recent back pains but was disappointed with a three-under par round 68 on a low scoring day at the Deutsche Bank Championship at TPC Boston on Friday. Woods, the FedExCup leader, was playing in the same group as leader Phil Mickelson, who shot a superb eight-under 63 after making seven birdies on his front nine. But the world number one was unable to match his playing partner's brilliance on the green, ending five shots behind Mickelson. "I don't think it was as good as I wanted. ... More...