BoxRec

15 rds Heavyweight
Jones was fast and gifted but 15 rds is a long time and while Jones might pile up some early rounds,Marciano will wear him down and begin to close in and stop him in the late rounds

At some point, Marciano goes upside Jones' head and it's all over.

Interestingly in the Ruiz bout Jones was on 5-7 pounds heavier of Rocky's regular weight.

In terms of boxing Roy had a huge advantage of speed, reflexes, skillset and technical abilities. He went the 12 round full distance without any problems not for a single time, a 15-rounder wouldn't be problematic either for such athlete.

Marciano was a bigger puncher and had a much better chin. Actually, puncher's chance seemed to be the only way of Rocky winning here. Yet it would be a big chance, acknowledging how shaky Roy's chin was. It's impossible to see Marciano outboxing Jones, but it's easy to see Rocky knocking Roy out cold.

Jones by wide dec or Marciano by KO at some point.

Roy had a fine chin before he moved down, Rocky could still KO him though. Jones Jr UD.

Very difficult for me to imagine Jones being actually able to beat Marciano. One boring unanimous decision over John Ruiz doesn't demonstrate to me he could have beaten any other heavyweight actually worth something, let alone a legitimate top ten heavyweight like Marciano who was incredibly conditioned and was throwing 80-120 power punches per round.

Marciano would hit him wherever he could and would not stop until he broke his arms, shoulders, etc--- until Jones was completely defenseless, just like he did Archie Moore and Ezzard Charles.

There is a reason why Roy Jones only fought once as a heavyweight and against the absolute weakest possible top heavyweight available. From my perspective James Toney and Tomasz Adamek ought to be given far and away more credit for their heavyweight adventures than Roy Jones.

Marciano kayo 8-10