World ranking: 33
US Open best:
2002: 1st round
2001: 1st round
2000: 1st round
Californian Alexandra Stevenson improved her ranking significantly last season, but remains an enigma.
She began last year outside the top 50 and ended inside the top 20, having reached her first WTA final and won more than 30 matches for the first time in her career.
But while the American has the ability to beat just about anyone on her day, she is just as likely to succumb to a baffling defeat.
Now 22 and still in search of her first trophy, she is struggling to find consistency this season.
Her best performance to date came in March, when she reached the semi-finals in Scottsdale.
Having rarely brought her A-game to Grand Slam events, Stevenson's most memorable achievement is reaching the last four at Wimbledon in 1999 - her first season as a professional.
But she has never won a match at the US Open, and a shoulder problem has hampered her preparations this year.