The writer would have to rely upon some extremely clever, or extremely shoddy cheats for Superman to win in a "fight" with Dr. Manhattan.
Ex: Something in Kal-El's Kryptonian physiology makes it impossible for Dr. Manhattan to molecularly disassemble him with a thought. If not, that's how such a contest would play out.
Ex: Superman flys around with tachyon emitters or lures Dr. Manhattan into a preselected area surrounded with tachyon emitters to prevent Dr. Manhattan from knowing his every move before he does. Example taken directly from Watchmen, which really only begs the question why Dr. Manhattan didn't simply disable the tachyon emitters. The answer is presumably he didn't have to, or he was simply too enthralled by the novelty of not knowing everything in advance for the first time since Osterman became Dr. Manhattan.
I could go on, but essentially Dr. Manhattan is a god in the truest sense of the word: he can make life out of nothing. He can turn matter into energy and energy out of matter. He could presumably create his own universe if he so desired.







