* Cards seven birdies in six-under 64 * Was unaware compatriot Park won Olympic gold * Cabrera-Bello in second place after 65 (Adds quotes, details) By Andrew Both GREENSBORO, North Carolina, Aug 20 (Reuters) - South Korean Kim Si-woo was focused intensely on his own task, birdying the final hole as he turned a narrow advantage into a four-shot lead after the third round at the Wyndham Championship on Saturday. Kim was almost flawless, carding a six-under-par 64 to move within sight of his first PGA Tour victory. More...