Serena Williams reacts after beating Victoria Azarenka, of Belarus, in the championship match at the 2012 US Open tennis tournament, Sunday, Sept. 9, 2012, in New York. (AP Photo/Charles Krupa)

NEW YORK (AP) -- Finally tested, even trailing, at the U.S. Open, Serena Williams turned things around just in time.

Two points from defeat, Williams suddenly regained her composure and her game, coming back to win the last four games and beat No. 1-ranked Victoria Azarenka 6-2, 2-6, 7-5 on Sunday night for her fourth championship at Flushing Meadows and 15th Grand Slam title overall.

Williams improved to 26-1 since a first-round exit at the French Open in late May, winning Wimbledon and the London Olympics.

It was the first three-set women's final in New York since 1995, and Williams came through with a late charge. She is the first woman to win Wimbledon and the U.S. Open in the same season since she did it a decade ago.