Ali sensed he needed a knockout to win .
Ali came out looking to land a put - away punch , but Frazier had n't taken a step back to that point , and he was n't about to do it now .
Sensing he needed a knockout to win , Ali came out looking to land a put - away punch , but Frazier had n't taken a step back to that point , and he was n't about to do it now .