It looked as though Williams was going to live up to her billing when she eased to the opening set with two breaks of Azarenka's serve.
The second of those breaks saw the American run out a 6-2 victor.
However, a double fault from Williams at the start of the second set handed Azarenka an early break. The Belarusian went on to hold her remaining service games, as well as securing another break to win through 6-2 and force a deciding third set.
Incidentally, since its opening in 1997, it was the first time that a third set had been played during the women's US Open final at the Arthur Ashe Stadium.
Azarenka gained control of the set when she broke for a 2-1 lead. That was soon wiped out by Williams though, who powered a forehand winner down the line to immediately level up the scores at two games apiece.
The third break of the set went the way of Azarenka, who opened up a 4-3 advantage in the process. She then her held her next service game to leave her just one game away from the second Grand Slam title of her career.
She failed to win any of the next three games though as 30-year-old Williams regained the lead by six games to five.
That left her serving to stay in the final. Having been taken to deuce by Williams, her experience appeared to come out on top as she forced Azarenka into hitting long on Championship point, thus giving her the 15th singles Grand Slam title of her career.