Sloane Stephens upsets Serena Williams at Australian Open

There are few moments when you can physically see the changing of the guard happening. One that comes to my golfing mind was Jack Nicklaus standing on the Swilcan Bridge, waving to the crowd during his last British Open as Tiger Woods was teeing off, prepared to win at St. Andrews.

And while this might be different as Nicklaus was past his prime, it had a little bit of the same feel. Sloane Stephens, a 19-year-old American who has the eyes to be a champion and the stamina to live up to it, was paired against Serena Williams, possibly the best American women's tennis player to ever hit a yellow ball on a court that has seen five trophy ceremonies set for Serena.

The match ended with Stephens upsetting the elder Williams 3-6, 7-5, 6-4, but there was plenty of action in between those numbers.

Williams dominated, struggled, left the court and broke a racket from start to finish, but it was the teenager who kept her cool the entire match and was able to leave the winner on Wednesday at Rod Laver Arena.

[Photos: Sloane Stephens upsets Serena Williams]

The match started out like you'd expect. Serena, who was a day removed from losing her doubles match with sister Venus in the quarterfinals, wasn't as aggressive as she normally is but allowed Stephens to make the mistakes late in an early set you might expect from someone trying to get to a point she's never been in a Grand Slam.

The set ended with Williams winning and was quickly opened with a break by Serena that had tennis fans expecting the expected. Williams would win, of course, and it was on to the next as the future American star would leave at the hands of our constant American champion.

But the second set would be the decider. After Sloane broke back, the set got to 5-3 with Stephens serving to take it to a third set but nerves finally settled in and as we've already seen in this Australian Open, a professional couldn't find the ability to finish off an opponent.

Williams would win that game, but it was when she was down 4-5 that Serena had to leave the court with what appeared to be that nagging ankle injury that upset her during her doubles match. Trainers later reported that Serena had suffered a back injury on a point close to the net that she put away, and it never seemed that Williams was the same.

After the match, Williams told reporters, "A few days ago (my back) got really tight and I had no rotation on it and I went for this drop shot in the second set and it locked up on it, and I couldn't really rotate after that."

Her first serve after returning to the court was a surprising 89 miles per hour, but Serena somehow held at love and forced Stephens to serve at 5-5. She held, and it was then that the teenager showed that she wouldn't let the hobbled Williams get away with just smashing winners at her discretion.

Stephens broke Serena to win the second set, and after holding at 2-1, Williams let some of her frustration out on a racket. She smashed it a few times on the court, saying after, "Oh yeah, did you see it? I even had a wry smile on my lips after that."

The match would slowly slip from Serena's grasp. She fought as hard as her injured back and ankle would let her, but eventually the young Stephens was too much, prevailing in the final set, saying after about advancing to the semifinals, "It's a new thing, but it's fun."

[Related: Li Na delivers one of pro tennis' worst serve at Aussie Open]

Stephens might still be a teenager, but she's incredibly talented and you see it in all parts of her game. Her fourth round win was solid but professional, and after she opened up on court like the 19-year-old she is.

She now faces the No. 1 seed in the tournament in Victoria Azarenka and most will expect her to lose but do you know the final thing she said in her post-match interview with ESPN before heading to the locker room?

"I hope to have a lot more Twitter followers, too!"

She's still 19, but her game is aging quickly.

Outside the Game from Yahoo! Sports:

Other popular content on Yahoo! Sports:
Grizzlies make a salary-cut trade, but it's not Rudy Gay
Kobe Bryant's frustration with Lakers' struggles grows
Tim Brown suggests Bill Callahan 'sabotaged' Raiders in Super Bowl XXXVII
Tiger Woods empathizes with Phil Mickelson over tax situation