NEW YORK (AP) — Kei Nishikori lost his focus. At least he didn’t lose the match. The seventh seed from Japan dropped a set, blew a lead in another and let four match points slip away before finally downing American Bradley Klahn 6-2, 4-6, 6-3, 7-5 on Wednesday to advance to the U.S. Open third round and avoid the pitfalls that have forced out half of the top 12 men’s seeds. Nishikori, a…