This is Williams' second Grand Slam of the year to go with a gold medal at the London Olympics.
Prior to the match, it would not have been a surprise if Williams was able to walk through this match with ease like she had done so often in the past couple of months. The American won at Wimbledon and followed that up with a dominant run at the Olympics to earn a gold medal.
In each of those tournaments, she had to face Azarenka in the semifinals. Williams came out with a victory in straight sets both times.
The first set of the U.S. Open final seemed to be more of the same as Serena won 6-2. She won 74 percent of her serves and added two aces for good measure. She also defended well as she won 50 percent of return points.
However, the No. 1 player in the world showed she deserved that ranking in the second set. When Williams struggled to get her serve in play, Azarenka jumped on it to take control of the match. She was solid on the returns and cross-court shots to win the set.
This forced Williams to the third set for the first time all tournament, and the first time since the Wimbledon finals in the beginning of July. She seemed out of energy and she started to lose her composure when it mattered most.
On the other hand, Azarenka has had plenty of experience in this position. Coming into the final, she won all 12 of her matches this season that went to three sets, including a win over Maria Sharapova in the semifinals.
However, that streak came to an end as Williams would just not give up. Despite being down five games to three in the final set, the 14-time Grand Slam champion showed great will and determination to come back. She served for the fourth game and then broke her opponent with the championship on the line. Two games later, she won her fourth U.S. Open title.
Two months ago, it seemed like the American's career was over. She was dealing with injury problems and had not won a major tournament in two years. Since then, she put that notion to bed as she is now back on top of the tennis world.
For Azarenka, there is no cause for concern. The 23-year-old won her first Slam at the Australian Open earlier this year and has been one of the most consistent performers in the sport. Her ability to finish off rallies make her the one person that was able to compete with Williams in recent months.
Tennis fans were given a treat with this final. Early upsets are fun, but it was magnificent to see two of the best in the sport compete in this evenly matched battle.