Suggested by Anonymous I’m afraid that while the One Above All is a rather strong cosmic being, his actual abilities have been open to debate for many years. The fact of the matter is….this guy is basically just an old man. I’m afraid that this is simply not good enough to try and take on someone like Captain Underpants. Captain Underpants may not have actual super powers, but he can still throw a mean punch and is actually in fairly good shape for an old guy. I think he would be able to surprise some people and win this fight. Captain Underpants wins.
DReager1.com 
“no actual superpowers”
Gonna correct you there. In the third book with the annoyingly long title, Underpants gets force fed Super Power juice while in the jaws of a dandelion. I know because I read them.
Oh, that’s good to know. Makes his win considerably easier then