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With every tournament Caroline Wozniacki wins—she's won four of her last five—it's becoming harder and harder to say that she's actually not the world No. 1.

Should we be saying something similar about Vera Zvonareva, the newly-minted No. 2 who's won 19 of her last 23 matches?

Serena Williams, 2010's dominant female player, has been out of the picture since Wimbledon. Obviously, that's a major reason why Wozniacki and Zvonareva are where they are in the rankings. But let's not discount the weight these two have pulled. As the top-ranked woman, Wozniacki hasn't melted under the spotlight—quite the opposite, it seems—and Zvonareva has been spectacular of late.

Today was one of her finest hours. Two hours, actually, in a 7-6 (4), 6-4 win, which puts Zvonareva at 2-0 for the Championships. The Russian rallied from first- and second-set deficits, and didn't crumble when the tide shifted Azarenka's way. In the first-set tiebreaker, a pivotal juncture of the match, Zvonareva let a 3-0 lead slip as she double-faulted up 4-2 to put the overtime back "on serve." Unfazed, she won three of the next four points to take the set.

Azarenka, playing her first match of the event, seemed to ride her momentum from winning last week's Kremlin Cup. She's now 0-1, but her form suggests she'll remain a threat in the White Group. A win over the struggling Jelena Jankovic seems likely; a win over Kim Clijsters would be immense.

As for Zvonareva? A win over Clijsters would be great, of course. Certainly possible. But she might not even need it to advance. Two match wins—old hat, for the new No. 2—gives her a bit of a cushion.

—Ed McGrogan