Dinara Safina knows she will have to be at the top of her game if she is to stand a chance of beating Serena Williams and claiming a place in the US Open final.
The sixth-seeded Russian will face No.4 seed Williams in Friday's semi-final, with the winner advancing to face either No.2 Jelena Jankovic or fifth-seeded Elena Dementieva in Saturday night's final.
Safina has not played a top-15 player en route to this stage of the hardcourt major, but that will change when she goes head to head with Williams, who has eight Grand Slam titles, including here in 1999 and 2002.
"She fights until the last, until the ball bounces two times on her side," Safina, who is chasing his first Grand Slam title, said.
"She moves very well and she can hit the ball from any position on the court very hard."
"So with her, you really have to be focused until the ball bounces two times or she misses or you hit a winner. That's why with her, you have to be alert every time."
While the 26-year-old Williams is the most decorated player remaining in the competition, Safina has been perhaps the best player on the WTA circuit in recently months.
The younger sister of former men's No.1 Marat Safin has won three titles and reached the final in six of the seven events she has played since the start of May, winning 37 of her 41 games.
Safina's outstanding run began in Berlin where she beat both former No.1 Justine Henin - who retired following the loss - and Williams before sinking Dementieva in the championship match.
She carried that momentum to the French Open where she defeated top-ranked Maria Sharapova en route to her first Grand Slam final, where she fell to current world No.1 Ana Ivanovic of Serbia.
Safina settled for silver at the Olympics as Dementieva beat her in the gold medal match, but the 22-year-old did see off Jankovic in the quarter-final in Beijing to become the first player to defeat three No.1 players in the same year.
Now Safina is in line to become No.1 herself if she wins this title and Jankovic - who held the top spot for seven days last month - loses to Dementieva in the semis.
Williams, Jankovic and Dementieva are all guaranteed top spot if they win the tournament.
Williams, who has won three and lost one of her games against Safina to date, is looking for her first Grand Slam title since capturing the 2007 Australian Open.
The 26-year-old American, who spent 57 weeks atop the rankings from 2002-03, has enjoyed another strong year with three titles, reaching the quarter-finals or better in 10 of 11 events.
Serena reached the final four on Wednesday with an tough 7-6 (8-6) 7-6 (9-7) victory over older sister Venus, who wasted 10 set points in the match.
Jankovic is the only player remaining who has never played in a Grand Slam final.
The 23-year-old Serb has won a title this year and has reached the quarter-finals or better in the 15 of 16 events, but she has been unable to get past the semi-final stage at Grand Slams.
And Jankovic will have her work cut out against Dementieva, who is also gunning for the first Grand Slam title of her career.
The Russian has quietly put together a great season and came into the