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In the past year we've seen Sam Stosur dominate Serena Williams in a U.S. Open final and crumble in a winnable French Open semi. The Aussie is like a box of chocolates, but her 6-2, 0-6, 6-4 loss to former junior star Arantxa Rus is still a great surprise, particularly after Stosur appeared to find her form.

Stosur's erratic nature may account for the strange scoreline of a match that's especially hard to explain. It was a contest of surges, and Stosur fired first, winning the first two games and earning two break points for a double-break advantage. Rus didn't just save both chances, she won the next six games—and then lost the next six.

When shifts this drastic occur, it's usually a result of both players' contributions, or lackthereof. That's precisely what happened to Stosur early on: She couldn't keep her forehand in the court consistently and failed to take advantage of her usually effective slice backhand, a shot made for grass. Although Stosur shook off this lapse once the second set began, the theme would resurface later.

Rus, who posted a major upset last year at Roland Garros when she beat Kim Clijsters, struggled with prosperity as the second set began. Her flat backhand, a shot she favors over her forehand, was unable to stay with Stosur's higher-bouncing forehands; Rus' momentum was drained like water in a bathtub. Once she surrendered the first three games, Rus appeared resigned to a third set, which is where things were quickly headed.

The game of runs continued, as Rus inexplicably won the first three games of set three, using her lefty forehand to counter Stosur's kick serve and force the favorite out wide. Of all the strokes hit today, this was the most effective. Stosur didn't strike a single ace until she was down 0-3, and sparked a mini-surge during which she broke back for 2-3.

But one push begets another, and Rus would break right back, followed by an error-filled return game that put Stosur in a 5-2 deficit. Fighting two battles throughout—one against Rus, the other with herself—Stosur never remained focused long enough. It may have been enough to skirt by Rus a year ago, but the Dutchwoman is quickly gaining experience in important pro tournaments; a return to the seeded days of her junior career seems likely.

I'm more confident in that assertion after watching how Rus closed things out. She earned two match points at 5-3, and after double-faulting on the first, she traded a barrage of shots with Stosur in one of the tournament's best rallies. It took perhaps Stosur's best shot of the day, a dive-bombing backhand targeted on the corner, to dispel Rus, who was eventually broken. But not for good—Rus remained focused and stayed on Stosur's backhand, a weak link all day, to elicit a number of errors at 5-4. One of them gave Rus her third match point, and when Stosur's subsequent slice backhand meekly caught the net, it was over.

Watching from home, I had been thinking to myself, 'Why isn't Stosur using the slice more?' Darren Cahill and Pam Shriver voiced my thoughts on the broadcast. It turned out to be the least effective stroke of them all today, just another day in the up-and-down singles career of Sam Stosur.