She now holds 17 Grand Slams spanning a total of 14 years.
The defending champion celebrated on the court with a series of jumping jacks after her opponent’s backhand sailed past on the second match point.
Williams took home US$3.6 million for the win – which includes a US$1 million bonus for prior events.
The match in detail
It had looked like it was going to be plain sailing for Williams after she won a difficult first set.
Then she let a double-break lead slip and failed to serve out the match twice during the thrilling, two and a half hour final.
Second seed Azarenka, 24, battled superbly, yet Williams regained her poise and dominated the final stages.
Afterwards Azarenka commented: “It’s a tough loss but being in the final against the best player, who deserves the win, it’s incredible … I gave it everything I had. I fought hard but well deserved. Congratulations Serena.”
A necessary win
After having won the French Open earlier this year, Williams admitted she “wasn’t happy with [her] performances in the other two Slams – and not even making it to the quarter-finals of one,” and would have felt disappointed with 2013 has it not been for this win; her fifth US Open title.
Prior to the match Williams had won eight titles and enjoyed a winning streak of 34 matches earlier in 2013.
But a quarter-final defeat at the Australian Open to Sloane Stephens and a fourth-round loss at Wimbledon to Sabine Lisicki left her feeling she needed another major title before the year was out – and this victory was firmly set in her sights.
Retirement still a long way off
This triumph means Williams now has 17 Grand Slam singles titles under her belt – one win behind sharing tied forth best with Chris Evert and Martina Navratilova – and seven short of Margaret Court’s all-time record of 24.
A slight change of direction has seen her working with French coach Patrick Mouratoglou since last year, and she insists retirement is a long way off.
“I feel great,” she said. “I have never felt better. I feel really fit. I can play a tournament like this, singles, doubles, with tough, tough schedules. For the most part, I felt really good.
“I haven’t felt like this in a number of years – I’m excited about the possibilities. I don’t know what can happen. I just keep playing and do the best that I can.”