I think Ali would outbox Rocky for most of the fight, but Rocky's constant pressure and debilitating hits just may wear out Ali in a 15-rounder. Marciano is like no other Ali faced.
Why ? he is not like Frazier ? Ali got 2:1 vs. Frazier and Marciano got badly cut against Charles. Remembering these Ali would most probably stop him late.
Ali has the jab to keep Marciano at bay and the strenghth to neutralize him inside. Ali UD or possible late stoppage due to cuts.
Why ? both stoppage wins were mostly rather an outcome of accumulated damage than a one punch. And yes , I also saw Walcott2 , but , I have also heard some opinions about it , Walcott was not young by then , and it was his last fight , and it was only one fight.
During the early 1980s, even a Marciano tribute magazine asserted that the Ali of the "Float like a Butterfly, Sting like a Bee" era would have cut Rocky up en route to a late round stoppage or lopsided decision win.
I always say, Marciano is the only one i consider to beat Ali, the only thing that puts me off is the size.
Ali would have to fight 3 minutes of every round against a fighter like Marciano..something he rarely did!!! No waving to the crowd...no shuffle....no head games against The Rock..they wouldn't work! Stoppage on cuts???...Rocky had a knack of coming up with the big punch when he needed it....I suspect that he would also in this fight...Marciano was a force of nature..he broke bones and bloodvessels....he hurt you no matter where he hit you....Marciano had a great heart... great chin....great conditioning and stamina....power in both hands..fought at a middleweights pace....never stopped coming....very awkward...you didn't know where the punches were coming from.....he had no concept of losing ...he had no concept of pain....in my opinion..you can't beat a fighter like that with a left jab...this is my all time "DREAM FIGHT"...I"ll take Marciano...
This is MY blueprint for the fight,also. Marciano would put up a good fight until he gets stopped late on.
Both in their primes? like an earlier poster remarked, it might depend on when they fought in regards to whether Ali cuts the face off rocky, or whether Ali beats him on pnts UD. Either way Ali wins in a by no means easy fight