All the ingredients are in place for a classic finish to the US Open women's singles tournament with a stellar cast set to take the court tomorrow in semi-final action at the year's final grand slam.

The four survivors include the winners of this year's three slams: Victoria Azarenka (Australian Open), Maria Sharapova (French Open) and Serena Williams (Wimbledon) as well as Roland Garros runner-up Sara Errani, who looms as the underdog after drawing Williams in the semis.

As the greatest player of her generation with 14 grand slam titles, Williams is the overwhelming favourite to beat Errani and is in great form, having won her fifth Wimbledon title in July then her first Olympic singles title.

She has already won the US Open three times, but only once since claiming her second title in 2002. Last year, she suffered a shock loss to Australia's Sam Stosur, but believes she is reaching her peak at the right time this week.

After a slow start, Williams has been steadily getting better with each match and is the only woman left yet to drop a set in the tournament.

"I feel like I'm going to get more focused and serious and start playing Serena tennis in the next couple of rounds," she said. "I didn't think I came into this tournament playing my best, but I definitely played better in the last two matches. I hope I have two matches left, and I can give it 200 percent."

Williams won her three previous clashes with Errani but the pair have not played each other since 2009, long before the Italian began her rapid move up the rankings.

"She's playing well. She made the final at Roland Garros and now semis here, potential finals," Williams said. "I can't underestimate her. It's not by luck she's been doing so well."

ENORMOUS CHALLENGE

The 25-year-old Errani is having the best season of her career. She has won four titles and made her first grand slam singles final at the French Open and climbed 35 places to be ranked 10th in the world.

She also won the doubles title in Paris and is through to the doubles final in New York, ensuring she will take over the world number one spot when the doubles rankings are released on Monday, but knows the enormity of the challenge she faces.

"Serena is playing unbelievable," Errani said. "I just have to go on the court and try to play my game the best I can."

While Williams is at short-odds to win her semi, there is no clear favourite between Azarenka and Sharapova. The pair have played each other nine times with Azarenka holding a 5-4 lead.

Azarenka beat the Russian in the final of this year's Australian Open to claim her maiden grand slam title and capture the number one ranking but Sharapova has already won a US Open, in 2006, and won the French Open in June to become just the 10th woman to win all four grand slam titles.

"She beat me in Australia quite easily and I would love to get my revenge at a grand slam," Sharapova said.

Azarenka is appearing in her first semi-final at Flushing Meadows and almost did not make it after she was pushed to a third set tiebreaker in her quarter-final with Stosur.

But she survived and the 23-year-old now has her sights set on beating Sharapova to make the final.

"Being in the semi-finals of the US Open for the first time is an incredible feeling for me but I definitely I don't want to stop," she said. "I'm going to do absolutely everything I have."

Head-to-head records of the 2012 US Open women's semi-finalists:

1-Victoria Azarenka (Belarus) v 3-Maria Sharapova (Russia) 2007 Moscow (Azarenka won 7-6 6-2) 2009 Los Angeles (Sharapova won 6-7 6-4 6-2) 2009 Beijing (Sharapova won 6-3 6-7 7-5) 2010 Stanford (Azarenka won 6-4 6-1) 2011 Miami (Azarenka won 6-1 6-4) 2011 Rome (Sharapova won 4-6 3-0 ret) 2012 Australian Open (Azarenka won 6-3 6-0) 2012 Indian Wells (Azarenka won 6-2 6-3) 2012 Stuttgart (Sharapova won 6-1 6-4) (Azarenka leads 5-4)

4-Serena Williams (US) v 10-Sara Errani (Italy) 2008 Rome (Williams won 6-4 6-3) 2009 Sydney (Williams won 6-1 6-2) 2009 Dubai (Williams won 4-6 6-2 6-0 (Williams leads 3-0)

Path to the women's semi-finals at the US Open (prefix denotes seeding):

1-Victoria Azarenka (Belarus) 1st round: beat Alexandra Panova (Russia) 6-0 6-1 2nd round: beat Kristen Flipkens (Belgium) 6-2 6-2 3rd round: beat 28-Zheng Jie (China) 6-0 6-1 4th round: beat Anna Tatishvili (Georgia) 6-2 6-2 Quarter-finals: beat 7-Sam Stosur (Australia) 6-1 4-6 7-6

3-Maria Sharapova (Russia) 1st round: beat Melinda Czink (Hungary) 6-2 6-2 2nd round: beat Lourdes Dominguez Lino (Spain) 6-0 6-1 3rd round: beat Mallory Burdette (U.S.) 6-1 6-1 4th round: beat 19-Nadia Petrova (Russia) 6-1 4-6 6-4 Quarter-finals: beat 11-Marion Bartoli (France) 3-6 6-3 6-4

Head to head: Azarenka leads 5-4

4-Serena Williams (US) 1st round: beat Coco Vandeweghe (US) 6-1 6-1 2nd round: beat Maria Jose Martinez Sanchez (Spain) 6-2 6-4 3rd round: beat Ekaterina Makarova (Russia) 6-4 6-0 4th round: beat Andrea Hlavackova (Czech Republic) 6-0 6-0 Quarter-finals: beat 12-Ana Ivanovic (Serbia) 6-1 6-3

10-Sara Errani (Italy) 1st round: beat Garbine Muguruza (Spain) 6-3 6-7 6-1 2nd round: beat Vera Dushevina (Russia) 6-0 6-1 3rd round: beat Olga Puchkova (Russia) 6-1 6-1 4th round: beat 6-Angelique Kerber (Germany) 7-6 6-3 Quarter-finals: beat 20-Roberta Vinci (Italy) 6-2 6-4

Head to head: Williams leads 3-0

Brief biographies of the women's semi-finalists at the 2011 US Open (prefix number denotes seeding):

1-Victoria Azarenka (Belarus)

Age: 23
Grand Slam titles: 1 (Australian Open 2012)

Won her maiden grand slam title at the Australian Open in January to move to the top of the world rankings for the first time as she started the season with a 26-match winning streak. Has won three other titles this year and a gold medal in mixed doubles at the London Olympics. Won the U.S. Open as junior in 2005 and is making her first appearance in the semis in the main event. Cruised through her first four matches in straight sets then survived a comeback from defending champion Sam Stosur in the quarter-finals before winning a third set tiebreaker.

3-Maria Sharapova (Russia)

Age: 25
Grand Slam titles: 4 (Australian Open 2008; French Open 2012; Wimbledon 2004; U.S. Open 2006)

Appearing in her first U.S. Open semi-final since winning the title six years ago as a teenager. She won the French Open in June to become just the 10th woman to win all four grand slam singles titles. Won tournaments in Stuttgart and Rome earlier this year and was a finalist at the Australian Open and London Olympics. Won her last two matches in three sets and has not lost any match this year that has gone the distance.

4-Serena Williams (US)

Age: 30
Grand Slam titles: 14 (Australian Open 2003, 2005, 2007, 2009, 2010; French Open 2002; Wimbledon 2002, 2003, 2009, 2010, 2012; U.S. Open 1999, 2002, 2008)

The greatest player of her generation, chasing her fourth U.S. Open title. Suffered a surprise defeat in last year's final to Australia's Sam Stosur but has been in great form in the past few months. She won her fifth Wimbledon title in July then the singles and doubles gold medals at the London Olympics. She is the only woman through to the semi-finals without dropping a set and is bidding to become the oldest woman to win the U.S. Open title since Margaret Court won aged 31 in 1973.

10-Sara Errani (Italy)

Age: 25
Grand Slam titles: 0

Made her first grand slam singles final at this year's French Open. Teamed up with her countrywoman Roberta Vinci to win the doubles title at Roland Garros. The pair are also through to Sunday's U.S. Open doubles final and Errani will become the number one doubles player in the world when the new rankings are released on Monday. Enjoying the best season of her career, Errani has won four titles and made her first U.S. Open semi but suffered an embarrassing moment at Wimbledon when she failed to win a single point in her "golden set" loss to Yaroslava Shvedova.

- Reuters