In 1970, when Ali returned to the ring, Joe Frazier was the undisputed heavyweight champion. He had won the WBA title in a unification bout against Jimmy Ellis.
Still in exile, Ali had been contacting Frazier and the two men had almost battled in a Philadelphia park.

Frazier’s management were the first to offer Ali a fight. He was supposed to box Frazier in his first post-exile bout. However, when Ali got a license in autumn of 1970, they drew back. So Ali boxed Jerry Quarry, a strong fighter with a good stamina. It was Ali's first fight in three-and-a-half years. He had just six weeks time to prepare for this fight.

In the first round of Ali vs. Quarry the audience saw a "floating" Ali who hit Quarry whenever he wanted. Quarry got better in the second round and landed some blows. After round three referee Perez ended the bout because of a huge cut above Quarry’s eye that was heavily bleeding.

After this not-convincing comeback, Ali faced Oscar Bonavena, a strong boxer from Argentina who Jose Torres describes in his book "Sting like a bee" as a 'stubborn donkey' because, after he had been hit, Bonavena would get even wilder and angrier and show not the least sign of weakness.
Ali ended a mediocre fight with an impressing last round knockout but with this couldn’t mislead the spectators that he lacked the speed that had provided for his successes before the layoff.

Then, at last, a championship bout against Joe Frazier was to take place. It was declared the "fight of the century". Ali lost a dramatic fifteen round battle on points and was defeated for the first time as a professional. The fight had a visible impact on the health of the two men. Both Ali and Frazier had to be x-rayed at hospital where some of Ali’s ribs showed contusions as a result of Frazier’s punches to the belly.
After this stunning defeat, Ali could book a very important victory. On June 28, 1971, his conviction of refusing to be inducted into the army was reversed and he got his passport and license back. The belt he had been stripped of could of course not be returned to him by the judges. Ali had to win it back on his own.

In the following 18 months, Ali won ten fights in a row with just one goal in mind: a rematch against Joe Frazier. His opponents were his friend Jimmy Ellis, Buster Mathis and the German Jurgen Blin in 1971, Mac Foster, again George Chuvalo and Jerry Quarry, Al Lewis, Floyd Patterson and Bob Foster one year later, and in 1973 Joe Bugner in Las Vegas.
Ali didn’t get more than § 500,000 for any of these bouts. His next opponent was to be Ken Norton, an absolute no-name. Ali didn’t take the fight too seriously and trained just three weeks.
This arrogance led to Norton breaking Ali’s jaw in the second round and winning the fight on points. It was incredible that Ali continued for ten rounds with a broken jaw but in the end it proved to be a fruitless effort. Ali was ahead by one point on the scorecards before the last round, but Norton won the last round and the fight.
After this defeat that had been even more painful than the one against Frazier, Ali was down on the floor and not many people thought that he could ever rise again.

Muhammad Ali, however, did not think about quitting. After his jaw was healed, he resumed training and prepared for the rematch against Ken Norton.