No one in Ali's camp that March 1971 night in Madison Square Garden – Ali included – had ever seen a fighter more determined than Joe Frazier. Frazier gave up 10 pounds in weight, four inches in height, and nine inches in reach. To win, he was going to have to penetrate Ali's long-range defenses. To penetrate, he was going to have to take some serious hits. To survive those hits, he was going to have to bob and weave from the waist, do it repeatedly, and do it all night, an exertion of nearly inhuman persistence and energy. [details (http://www.boxingscene.com/?m=show&id=3326)]

Everyone says that there last fight was the best of the three, but i personally liked the first. Though they both gave all they had in all three.
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I thought the first fight was the best of the three, while the third was the most brutal.
The final one was probably the fiercest heavyweight fight I have seen that went that long.