SAN FRANCISCO — The U.S. Open won Webb Simpson on Sunday at the Olympic Club. Someday, maybe even Monday morning, he’ll wake up and ask, “How did that happen?” Actually, he’s already asking it and he doesn’t have an answer. Not that he cares. He’s too busy grinning, reading the 135 texts on his phone and, in his disarming way, sharing the marvelous mysterious magic — sometimes it really is that corny — of these mischievous U.S.