By Richard Pagliaro, Tennis.com

Victoria Azarenka (1) vs. Samantha Stosur (7)
Head-to-Head: Azarenka leads, 6-0

What Stosur needs to do to win:
Serve boldly (her 26 aces are second most in the tournament) and try to end points on the first strike when her serve elicits a short reply. Once the baseline rallies are neutral, Azarenka has the edge, because she’s more balanced off the forehand and backhand. Stosur must impose her serve-and forehand combination and vary the height of her shots—mix her shoulder-high bounding forehand with some low slice backhands—to try to unsettle the Belarusian.
 
What Azarenka needs to do to win:
Impose her significant advantage on the backhand side—Azarenka’s two-handeder is one of biggest weapons in the game—by attacking Stosur’s weaker backhand wing. Exploit the Aussie’s habit of running around her backhand to hit her forehand by driving her own backhand down the line at times. Rip returns off second serves: Azarenka has broken serve a tournament-best 25 times in four matches.
 
The Pick: Azarenka in two sets
Defending champion Stosur has won 11 consecutive U.S. Open matches, but Azarenka has been a nightmare opponent, winning all 12 sets they’ve played on hard courts. Stosur’s heavy topspin has not fazed the six-foot Azarenka, who handles the high ball well; Vika's two-handed backhand has terrorized Stosur in the past. Stosur is a former top-ranked doubles player who will need to use her variety, but this match is in Azarenka’s hands.
 
Marion Bartoli (11) vs. Maria Sharapova (3)
Head-to-Head: Sharapova leads 4-0

What Bartoli needs to do to win:
Get off to a fast start and try to attack Sharapova’s second serve to plant some doubt in the 2006 champion’s mind. Bartoli has not won a set in four prior meetings with Sharapova, so a fast start is critical for her confidence. Try to tie up her tall opponent with some occasional deep drives down the middle to diminish her access to angles.
 
What Sharapova needs to do to win:
Take the first strike effectively and work deep, cross-court drives to exploit the limited reach of the 5’6” Frenchwoman, who plays with two hands off both sides. Sharapova has commanded the center of the court in their past meetings, making Bartoli run and creating openings for her down-the-line drives, a tactic she should apply in their quarterfinal meeting.
 
The Pick: Sharapova in two sets
Given her past dominance of this match-up, Sharapova should carry a lot of confidence into this quarterfinal. Both are aggressive baseliners, but Sharapova possesses more power, owns a more penetrating serve, and is 11-0 in three-set matches this year. Sharapova has won 23 of her last 25 matches, and barring a serving collapse should continue her mastery of Bartoli.
 
Serena Williams (4) vs. Ana Ivanovic (12)
Head-to-Head: Williams leads 3-0

What Ivanovic needs to do to win:
Serve exceptionally well and stay aggressive. Ivanovic served under 50 percent in two of her four tournament wins, and must serve above 60 percent against Serena. The 2008 French Open champion is not as quick around the court as Williams, so she cannot allow herself to be dragged into defensive positions. Ivanovic must be cracking her favored forehand with accuracy and ambition to have a shot at the upset.
 
What Williams needs to do to win:
Maintain the focus and ruthlessness she’s displayed throughout the tournament, use her cross-court backhand to break down Ivanovic’s weaker backhand wing, and try to engage the slower Serbian in running rallies. Serena is the more accurate and explosive ball striker on the run, so she will want to play cross-court shots early to move Ivanovic side-to-side. Williams should attack Ivanovic’s second serve, as the world No. 13’s toss can stray wide when she’s stressed.
 
The Pick: Williams in two sets
This is a clash of former world No. 1s, but Serena is better in every element of the game and has had Ana’s number in winning all six sets they’ve played, including a pair of victories at the U.S. Open in straight sets. Serena has won 24 of her last 25 matches, three of the eight sets she’s played at love, has only dropped serve twice all tournament—and is hungry to win her first U.S. Open title since 2008.
 
Sara Errani (10) vs. Roberta Vinci (20)
Head-to-Head: Errani leads 3-2

What Errani must do to win:
The French Open finalist should use her heavy topspin to try to pin her doubles partner behind the baseline and provoke short balls. A consistent and accurate baseliner who reached the Australian Open quarterfinals in January, Errani is at her best playing longer, grinding rallies and should try to engage Vinci in lengthy exchanges.
 
What Vinci must do to win:
Use her greater variety of shots and aggressive court positioning to apply pressure. Vinci is a skilled all-court player who can flatten out her forehand but also attack net behind the slice backhand. The 29-year-old Italian, who partnered Errani to win the French Open doubles title, will want to attack any shots that land short in the court and close points at net.
 
The Pick: Vinci in three sets
They are doubles partners and best friends who know each other’s games so well that it will be tough for either woman to surprise the other. Errani is contesting her third major quarterfinal of the season, while Vinci is playing the first major quarterfinal of her career, so we know who has the experience. But Vinci should be confident after sweeping second-ranked Agnieszka Radwanska, and her all-court skills and ability to take the ball earlier makes her the pick.