Factbox: Serena Williams v Victoria Azarenka

(Reuters) - A look at the key facts and records of American Serena Williams and Belarus’ Victoria Azarenka before their U.S. Open semi-final on Thursday (prefix number denotes seeding):

3-SERENA WILLIAMS

Age: 38

WTA ranking: 8 (Highest ranking: 1)

Grand Slam titles: 23

Career WTA titles: 73

2019 U.S. Open performance: Runner-up

Best U.S. Open performance: Champion (1999, 2002, 2008, 2012, 2013, 2014

ROAD TO SEMI-FINAL

First round: Kristie Ahn (U.S.) 7-5 6-3

Second round: Maragarita Gasparyan (Russia) 6-2 6-4

Third round: Sloane Stephens (U.S.) 2-6 6-2 6-2

Fourth round: 15-Maria Sakkari (Greece) 6-3 6-7(6) 6-3

Quarter-finals: Tsvetana Pironkova (Bulgaria) 4-6 6-3 6-2

Williams is a six-times U.S. Open champion but has not triumphed at Flushing Meadows since 2014. She has been made to work hard for her victories this year, dropping a set in three of her five matches so far.

Williams holds an 18-4 lead over Azarenka and defeated the Belarusian in the U.S. Open final in 2012 and 2013.

VICTORIA AZARENKA

Age: 31

WTA ranking: 27 (Highest ranking: 1)

Grand Slam titles: 2

Career WTA titles: 21

2019 U.S. Open performance: First round

Best U.S. Open performance: Runner-up (2012, 2013)

ROAD TO SEMI-FINAL

First round: Barbara Haas (Austria) 6-1 6-2

Second round: 5-Aryna Sabalenka (Belarus) 6-1 6-3

Third round: Iga Swiatek (Poland) 6-4 6-2

Fourth round: 20-Karolina Muchova (Czech Republic) 5-7 6-1 6-4

Quarter-finals: 16-Elise Mertens (Belgium) 6-1 6-0

Azarenka is in the semi-finals of a Grand Slam for the first time since 2013.

The Belarusian, who won her first title in four years at the Western & Southern Open last month, has won just four of 22 meetings against Williams and is yet to defeat the American in a Grand Slam.

HEAD TO HEAD: Williams leads 18-4

2019 Williams d Azarenka 7-5 6-3 (Indian Wells, hard)

2016 Azarenka d Williams 6-4 6-4 (Indian Wells, hard)

2015 Williams d Azarenka 3-6 6-2 6-3 (Wimbledon, grass)

2015 Williams d Azarenka 3-6 6-4 6-2 (French Open, clay)

2015 Williams d Azarenka 7-6(5) 3-6 7-6(1) (Madrid, clay)

2014 Williams d Azarenka 6-4 7-5 (Brisbane, hard)

2013 Williams d Azarenka 7-5 6-7(6) 6-1 (U.S. Open, hard)

2013 Azarenka d Williams 2-6 6-2 7-6(6) (Cincinnati, hard)

2013 Williams d Azarenka 6-1 6-3 (Rome, clay)

2013 Azarenka d Williams 7-6(6) 2-6 6-3 (Doha, hard)

2013 Williams d Azarenka W/O (Brisbane, hard)

2012 Williams d Azarenka 6-4 6-4 (WTA Championships, hard)

2012 Williams d Azarenka 6-2 2-6 7-5 (U.S. Open, hard)

2012 Williams d Azarenka 6-1 6-2 (London Olympics, grass)

2012 Williams d Azarenka 6-3 7-6(6) (Wimbledon, grass)

2012 Williams d Azarenka 6-1 6-3 (Madrid, clay)

2011 Williams d Azarenka 6-1 7-6(5) (U.S. Open, hard)

2011 Williams d Azarenka 6-3 6-3 (Toronto, hard)

2010 Williams d Azarenka 4-6 7-6(4) 6-2 (Australian Open, hard)

2009 Williams d Azarenka 6-2 6-3 (Wimbledon, grass)

2009 Azarenka d Williams 6-3 6-1 (Miami, hard)

2009 Williams d Azarenka 3-6 4-2(ret) (Australian Open, hard)

2008 Williams d Azarenka 6-3 6-4 (Australian Open, hard)