Stosur kept her composure as Williams erupted in anger at the chair umpire in the second set, dominating the 13-time Grand Slam champion who had reached the final without dropping a set.
She became the first Australian woman to take the title in New York since Margaret Court in 1973, and the first to win a Grand Slam title since Evonne Goolagong won Wimbledon in 1980.
"I had one of my best days and I'm very fortunate that I had it on this stage in New York," Stosur said.
"Ever since I started playing it was a dream of mine to be here one day." Williams arrived in the final after
dismantling world number one Caroline Wozniacki in the semifinals on Saturday night. But Stosur, playing her second career Grand Slam final after a runner-up finish in the French Open last year, quickly claimed the opening set, breaking Williams to lead 2-1 and winning the last 12 points of the set as Williams' frustration grew.
Williams, whose powerful serve is a cornerstone of her game, struggled to get her first serves in and Stosur
repeatedly made her pay. The Australian was still rolling in the opening game of the second frame, giving herself a double break point with a crushing return of serve. Williams saved one with an ace, and
appeared to save another for deuce.
But the American's shout of "c'mon" as soon as she unleashed her forehand came before Stosur reached the ball, and umpire Eva Asdaraki immediately penalised Williams for "intentional hindrance"and the point and the game went to Stosur. "Aren't you the one who screwed me over last time?," Williams bellowed at Asdaraki. "That is totally not cool." The scene recalled Williams' similar meltdown in her 2009 semifinal defeat to Kim Clijsters. In that match, she unleashed a tirade of abuse at a lineswoman who called a foot-fault during the tense match and a penalty point sealed her fate in a 6-4, 7-5 defeat.
This time an angry Williams -- backed by a suddenly energized crowd on the 22,000-seat Arthur Ashe Stadium -- immediately stepped up her game, breaking Stosur for 1-1 and holding to edge ahead 2-1.
Williams continued to berateAsdaraki on the changeover, but Stosur stayed calm and saved two break points in the fourth game tolevel the set at 2-2.
Stosur said she didn't really know just what was happening between Williams and Asdaraki. "I was just kind of there," Stosur said. "I do know the rule, but it's not something I've ever had to deal with before." She gained the edge with a break for 4-3, and broke again to seal the match with yet another blistering return off a Williams second serve on her third match point.
"I don't really know what to say," said Stosur, whose rugged path to the final included a third-round victory over Nadia Petrova that lasted a US Open women's record three hours and 16 minutes and a marathon 17-15 tiebreak loss to Maria Kirilenko before she rallied to beat the Russian. "Serena, you are a fantastic player, great champion and have done wonders for our sport. Thanks to everyone back home for supporting me. All my friends, family and everyone else, thanks so much for supporting me. I look forward to coming back home," said Stosur.
When it was all over, Williams congratulated Stosur, and did her best gloss over her burst of temper."I was doing my best," she said. "I hit a winner but I guess it didn'tcount ... But it wouldn't have mattered anyway because she played really well."
