I guess you'd have to belive that Dempsey would out-manuever Frazier early and hurt him. But Frazier is extraordinarily resiliant. I don't think that Dempey could ditch Frazier Foreman-style which means that he would have a chance to work his way back into contention in the middle rounds. But I don't think he could drag his way back into this one. I'd look for the referee/Frazier's corner to rescue Joe around 10.
I'm going to say Dempsey probably by TKO late. I think he had the better chin and better power in either hand.
Joes left hook was hands down the best overall, delivery, speed, power.. But when it comes to straight up power, i still say Tuas hook is the strongest i've seen..
I think that Frazier would win surprised nobody else seems to think so he was bigger had better stamina and faced the much better opponents who has Dempsey beaten who can compare to Ali.
Dempsey takes this one. Height, reach, speed, two handed power, mobility, chin. Jerry Quarry proved that it was possible to hook with Frazier at Joe's best, and outfight him on the inside while outworking him to the body(although Jerry was only able to sustain that for the first couple rounds of their inaugural tussle). However, that could well be all the time Dempsey needed with his firepower, especially if Jack landed on Smoke the way Quarry started out doing. Frazier would also need to be mindful of that right uppercut Dempsey put out Firpo with, as Jack was backed against the ropes. However, Joe can make things very uncomfortable for Dempsey if he can make Jack box tall. Frazier was considerably shorter than his predecessor, who preferred to remain lower than his opponents. Tommy Gibbons not only made Dempsey box taller, but he was also able to smother Jack's punches on the inside, before Dempsey was able to generate any steam behind those shots. It would be imperative for Frazier to do this. Joe would also need to maintain continual forward movement. If Dempsey was doing the advancing, the competitive phase of the bout would be over for Joe. Smoke would be better off getting Jack moving laterally, counterclockwise towards Joe's hook, requiring skilled ring generalship on Frazier's part. Joe's braintrust of Durham and Futch would devise the appropriate strategy to achieve this. A major consideration has to do with what happens if Frazier gets hurt. Whenever Dempsey was stunned, he was practiced and skilled at clinching for the few seconds necessary to recover (having a servicable wrestling background to draw upon). But this is not a tactic we see Joe employ after the knockdowns he sustained against Bonavena and Foreman. (I'm going to assume the three knockdown rule is waived for this one. Frazier would likely need that waiver.) For Frazier to win, he'd have to go the distance. Is that possible? In his title defense against Quarry, he was more relaxed and better paced as the match continued, and even if Jerry had not sustained any facial damage, it appeared that he would have wound down as the rounds passed, with Frazier maintaining even pressure until forcing a stoppage (in much the same way Quarry wore down before getting stopped in his rematch with Ali). Dempsey demonstrated his late round finishing power in the title fight rematch with Brennan, and would remain potentially lethal throughout. But Joe's best chance would still be to drag Jack into deeper water, then forge ahead in the scoring. I don't think Smoke would last that long though. Even if Frazier gets out of the opening rounds, he would have probably sustained enormous damage by that point. Dempsey was much faster than Foreman, and IMHO, Jack was the hardest punching heavyweight champion in history. (I rate Shavers as the hardest punching heavyweight overall.) With Joe unable to tie Dempsey up when essential to do so, I figure a fourth or fifth round stoppage would result, either by the referee, or Frazier's corner (over Joe's vehement protestations, of course).
Frazier was arguably a slow starter and that is suicide aginst Dempsey. Forgett George Foreman and Joe Louis. Dempsey was the most dangerous heavyweight champion in the first three rounds of a fight.
I think Frazier would win if it gets beyond 4 rounds, which I think it would. Whilst Dempsey was fast, aggresive and powerful, he was innacurate. I think he'd miss the majority of the punches he would throw against Frazier. Despite hitting him several times, Frazier wouldn't be too bothered by those punches. After the fight goes on, Frazier being the better boxer shows. He would outbox Dempsey and make him look foolish knocking him down several times. After about 11 rounds, Frazier would finally stop Dempsey.