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Third fight against Joe Frazier

Ali then agreed to a third match with Joe Frazier in Manila. The bout, known as the " Thrilla in Manila ", was held on October 1, 1975, in temperatures approaching 100 °F (38 °C). In the first rounds, Ali was aggressive, moving and exchanging blows with Frazier. However, Ali soon appeared to tire and adopted the "rope-a-dope" strategy, frequently resorting to clinches. During this part of the bout Ali did some effective counterpunching, but for the most part absorbed punishment from a relentlessly attacking Frazier. In the 12th round, Frazier began to tire, and Ali scored several sharp blows that closed Frazier's left eye and opened a cut over his right eye. With Frazier's vision now diminished, Ali dominated the 13th and 14th rounds, at times conducting what boxing historian Mike Silver called "target practice" on Frazier's head. The fight was stopped when Frazier's trainer, Eddie Futch, refused to allow Frazier to answer the bell for the 15th and final round, despite Frazier's protests. Frazier's eyes were both swollen shut. Ali, in his corner, winner by TKO, slumped on his stool, spent.

An ailing Ali said afterwards that the fight "was the closest thing to dying that I know", and, when later asked if he had viewed the fight on videotape, reportedly said, "Why would I want to go back and see Hell?" After the fight he cited Frazier as "the greatest fighter of all times next to me".

After the third fight with Frazier, Ali considered retirement. He said, "I'm sore all over. My arms, my face, my sides all ache. I'm so, so tired. There is a great possibility that I will retire. You might have seen the last of me. I want to sit back and count my money, live in my house and my farm, work for my people and concentrate on my family."