(Untitled)

Two points from defeat, Williams suddenly regained her composure and her strokes, coming back to win the last four games and beat top-ranked Victoria Azarenka, 6-2, 2-6, 7-5, Sunday night for her fourth championship at Flushing Meadows and 15th Grand Slam title overall.

‘‘I honestly can’t believe I won,’’ Williams said during the trophy presentation after the 2-hour-18-minute match. ‘‘I really was preparing my runner-up speech, because I thought, ‘Man, she’s playing so great,’ I’m really shocked.’’

Might be the only one.

After all, what really was stunning was that Azarenka made things as interesting as they were, given that she came into the day 1-9 against Williams over their careers.

Add in that Williams hadn’t dropped a set in the tournament, losing only 19 games through six matches before Sunday. All part of a tremendous run she is putting together in reaction to her loss at the French Open in late May, the American’s only first-round exit in 49 career major tournaments. Since then, she is 26-1, winning Wimbledon and the London Olympics.

There hadn’t been a three-set women’s final in New York since 1995, and Williams came through with a late charge to become the first woman to win Wimbledon and the US Open in the same season since a decade ago, when — yes, that’s right — she did it.

‘‘Serena deserves the win. She showed how true of a champion she is,’’ said Azarenka, who managed only 13 winners, 31 fewer than Williams. ‘‘I definitely gave it all today. Stepping out of this court today, I will have no regrets.’’

Azarenka hadn’t dropped a three-set match all season until Sunday, going 12-0 in matches that went the distance, including victories over defending US Open champion Sam Stosur in the quarterfinals and 2006 champion Maria Sharapova in the semifinals.

As the third set commenced, Williams’s mother, Oracene Price, told her from the stands, ‘‘Settle down.’’

Didn’t happen right away.

When Williams double-faulted, slapped a bad backhand into the net and pushed a forehand long, Azarenka broke at love for a 4-3 edge, then followed that up by holding for 5-3.

One game from the championship.

Azarenka was 2 points away at 30-all with the fourth-seeded Williams serving in the next game, but couldn’t convert. And when Azarenka served for the victory at 5-4, she showed the jitters that probably are understandable given that this was only her second career Grand Slam final, 17 fewer than Williams.

Azarenka made three errors in that game, including a forehand into the net that let Williams break her to 5-all. Williams kept whatever excitement she might have felt contained, face straight as possible, while her older sister, Venus, smiled and clapped in the stands.

That was during a key stretch in which Williams took 10 of 12 points to go ahead, 6-5. She then broke again to win, dropping onto her back on the court when Azarenka sent a backhand long to end it.

Azarenka slumped in her changeover chair, a white towel covering her head, as Williams kept saying, ‘‘Oh, my God! Oh, my God! Oh, my God!’’ while scurrying over to share the joy with her mother and big sister.

Williams, who turns 31 Sept. 26, is the first 30-year-old woman to win the US Open since Martina Navratilova in 1987.

She won her very first major championship at age 17 at the 1999 US Open. Winning titles 13 years apart at the same Grand Slam tournament represents the longest span of success in the professional era, which began in 1968.