Complex sentence: But the Bills-Patriots Eastern Division playoff wasn't played until after the season (on Saturday, December 28th, the day before the Chicago-New York NFL Championship Game), thus pushing the Boston-San Diego championship game until January 5,1964.
Split into simpler sentences: But the Bills-Patriots Eastern Division playoff wasn't played until after the regular season ended, being played on Saturday, December 28th (the day before the Chicago-New York NFL Championship Game). This meant that the Boston-San Diego championship game wasn't played until January 5,1964.