Serena Williams' awe-inspiring comeback has suffered a shocking setback – the champion's 12-match winning streak has been cut short by a retirement! It might be Serena's tactical decision to prevent her from exhaustion or injuries ahead of the US Open, but it still is disappointing that her string of victories is ending in such a way. Serena retired with a right toe injury prior to her second-round match against Samantha Stosur at the Western & Southern Open.

After almost a year away with injuries and illness, Serena returned like a storm, winning Stanford and Toronto and following it up with a victory against Lucie Gradecka in the first round of Cincinnati this week.

Update: Here's Serena's press conference following the withdrawal.

(photo courtesy of FIJI Water)

Caroline Wozniacki’s form ahead of the US Open is becoming worrying – the Dane suffered her second straight loss in an opening match and not even the presence of her rumored boyfriend Rory McIlroy did her good today against Christina McHale, an American ranked 75 placed below her.

In the second round of the Western & Southern Open, McHale broke Wozniacki’s poor serve five times during the two-set encounter which finished 6-4 7-5. Last week at Toronto Wozniacki lost her opening match against Roberta Vinci with the same score.

The world No.1 has lost only 12 matches this season, but early exists have piled up recently, including her retirement against Sofia Arvidsson in the second round of Bastad last month. (photo: © Neal Trousdale)

In the beginning it seemed Serena Williams would cruise to a quick victory over world No.49 Lucie Hradecka in the first round of the Western & Southern Open in Cincinnati, as the American stormed through the first set with a 89% of first serve points won.

However, at 5-1 down in the second set, the Czech fired back and frustrated Serena when she leveled at 5-5 by breaking the American's serve twice. The tiebreak was played, but Hradecka had an unglamorous finish when she lost the tiebreak 7-5 with a double fault.

Both players hit 31 winners, but Hradecka committed more unforced errors. Final score: 6-3 7-6(5).

Serena's rankings improved on Monday from No.80 to No.31 following her triumph at the Rogers Cup. Together with her Stanford title, Serena is now on a 12-match winning streak. (photo: © Neal Trousdale)

Tenth seed Maria Sharapova wasted three match points as clouds were approaching Cincinnati and didn’t manage to be faster than the rain, so her final against fourth seed Kim Clijsters got suspended at 6-2 5-3 with Clijsters serving on deuce. You know how these rain delays can bring a turnaround and that's exactly what happened. When play resumed, Clijsters took charge, won three successive games, soon after the tiebreak 7-4 and the deciding set 6-2. The victory slipped through Sharapova's fingers and on top of everything she even needed a medical timeout for her ankle. Final score: 2-6 7-6(4) 6-2.

The world No.7 Clijsters has become the first WTA player this year to win three titles: Brisbane, Miami, and now Cincinnati. The Belgian improved to 4-0 in finals since her comeback and is now 38-17 in career finals.

En route to the Western & Southern Financial Group Women’s Open title Clijsters defeated Dinara Safina in the second round, Christina McHale in the third, seed No.11 Flavia Pennetta in the quarterfinals, Ana Ivanovic in the semifinals, and finally the three-time Grand Slam champion Sharapova.

By winning the Cincinnati title Clijsters earned $350,000, while Sharapova earned $175,000 as runner-up. (photo: © Neal Trousdale)

Ana Ivanovic’s promising return to form in Cincinnati was making all the headlines and unbelievably all the hope of her resurgence got a bitter tone as the Serb retired injured from her semifinal against Kim Clijsters after playing just three games. We could have expected a meltdown, nerves, bad play, or whatever, but an injury! No way!

Ivanovic was trailing 2-1 when she made a return and hurt her ankle. She then received treatment and got back to the court, but couldn’t continue with the match. Nevertheless, the world No.62 Ivanovic will return to the Top 40 in the new rankings, but if the injury turns out to be serious she could well slip again. I hope the future will be favorable to Ana.

Clijsters’ opponent in the final will be the winner of the match between Maria Sharapova and Anastasia Pavlyuchenkova. (photo: © Neal Trousdale)