Williams did not drop a set throughout the tournament
Serena Williams saw off a valiant display from Serbia's Jelena Jankovic to win her third US Open title and regain the world number one ranking.
The American, 26, came through 6-4 7-5 in a fantastic match to secure her ninth Grand Slam title.
Jankovic, 23, was playing in her first Grand Slam final but made the better start before Williams fought back with three breaks to win the opening set.
And Williams sealed victory after saving four set points in the second.
"I'm so excited," she said. "This was magical. It was everything coming together like magic.
"I wasn't even going for number one and it's just like an added bonus. It is that special because I've been working so hard."
Williams has now won one French Open, two Wimbledon, three Australian Open and three US Open titles, adding to her victories of 1999 and 2002 in New York.
For me to be in the finals was a great achievement
Asked to compare this US Open to the other two, Williams said they are all special in their own way.
"Each one means a lot," she said. "The 1999 one was special because I knew I was going to win it. I just felt it.
"I wanted it so bad in 1999. It was my first Grand Slam so no one can take that away. I won doubles that year too."
The final had been rescheduled after the remnants of tropical storm Hanna forced a postponement from Saturday for the first time since 1974.
It was worth the wait, with both players lurching between world-class winners and desperately nervous errors in a matter of moments.
Grand Slam final debutante Jankovic made the more confident start, breaking as early as game three, but Williams recovered from 0-40 in the following game to level.
An ill-timed Jankovic double-fault contributed to another break of serve two games later but Williams failed to serve out at 5-3, netting a backhand on the third break point of the game.
All Jankovic's good work was undone almost immediately, however, when she fell 0-40 down in the following game and sent a forehand long on the second set point.
If the first set had been unpredictable, the second set was something else entirely.
Williams looked in charge with two break points in game two but failed to convert and it was exactly the same story in game six as the American seemed to be struggling physically.
And after the first of several Jankovic complaints to the umpire over how long her opponent was taking between points, the Serb moved 4-3 ahead with a break when Williams played a terrible drop shot at break point down.
Williams appeared to be tiring dramatically but then launched an astonishing comeback, recovering from 0-40 to save three set points when serving at 5-3 down.
The game of the match, and arguably the tournament, followed as Williams stormed 0-40 clear in game 10 before making three unforced errors.
Another Jankovic set point and a total of five break points would go begging before Williams finally levelled with a forehand winner.
A lunging backhand volley saw the former champion hold serve in the next game before Jankovic saved a first championship point with a forehand winner.
With the chance to force a tie-break in front of her, however, Jankovic double-faulted.
And when a second championship point came around moments later, her backhand error handed Williams back the title she last won six years ago, as well as the number one ranking.
"I was proud to be in the finals but I'm always disappointed when I lose," said Jankovic.
"Serena was a better player tonight. Congratulations to her for winning the whole tournament. She was just too good.
"I really had a lot of injuries and struggled throughout the year with my health. For me to be in the finals was a great achievement."