NEW YORK (AP) - Already outplayed by Sam Stosur in the U.S. Open final, the last thing Serena Williams needed was to lose a game for yelling during a point.

That's exactly what happened early in the second set, leading to an argument between Williams and the chair umpire, a scene less ugly than - but reminiscent of - the American's tirade two years ago at the same tournament. In the end, Stosur beat Williams 6-2, 6-3 Sunday in a surprisingly lopsided upset for her first Grand Slam title.

"I think I had one of my best days," Stosur said. "I'm very fortunate to do it on this stage."

Hitting powerful strokes from the baseline, and looking fresher than the far-more-accomplished Williams right from the start, the ninth-seeded Stosur became the first Australian woman to win a major championship since Evonne Goolagong Cawley at Wimbledon in 1980.

"She played really, really well. She's a great player, and it's good to see," Williams said. "I tried my hardest and she kept hitting winners and I was, 'Oh my God, what am I doing?'"

This was only the 27-year-old Stosur's third title at any tour-level event, and what a way to do it. She took advantage of Williams' so-so serving and stayed steady throughout - finishing with 12 unforced errors to Williams' 25 - despite the bizarre events that unfolded in the second set.

Indeed, the biggest victory of Stosur's career so far likely will be recalled by everyone else for Williams' latest dispute with an official at Flushing Meadows.

Down a set and facing a break point in the first game of the second, the 13-time major champion hit a forehand and shouted, "Come on!" as Stosur reached down for a backhand. Chair umpire Eva Asderaki ruled that Williams hindered Stosur's ability to complete the point and awarded it to Stosur - putting her ahead 1-0 in that set.

Williams went over to talk to Asderaki, saying, "I'm not giving her that game."

Williams also said: "I promise you, that's not cool. That's totally not cool."

Some fans began booing, delaying the start of the next game as both players waited for the commotion to subside.

Tournament director Brian Earley said Asderaki's ruling was proper.

But Williams had trouble putting the whole episode behind her.

During the changeover two games later, Williams continued to talk to Asderaki, saying, "You're out of control. ... You're a hater, and you're just unattractive inside. ... And I never complain. Wow."

Williams also told the official: "Really, don't even look at me."

When Stosur wrapped up the match with a forehand winner, Williams refused the customary post-match handshake with the chair umpire.

"I hit a winner, but I guess it didn't count," Williams said during the trophy presentation. "It wouldn't have mattered in the end. Sam played really well."

This sort of thing has happened before at the U.S. Open to Williams, who won the tournament in 1999, 2002 and 2008.

In the 2009 semifinals against Kim Clijsters, Williams was called for a foot-fault that set her off on a profanity-laced outburst at a line judge. Williams lost a point there, and because it came on match point, Clijsters won. That led to an immediate $10,000 fine from the U.S. Tennis Association and later a record $82,500 fine from the Grand Slam administrator, who also put Williams on a "probationary period" at Grand Slam tournaments in 2010 and 2011.

A poor call during Williams' 2004 U.S. Open quarterfinal loss to Jennifer Capriati was cited as a main reason for the introduction of replay technology in tennis.