Top seed Maria Sharapova says she will have to be sharper in her next match if she is to reach the US Open final.
"I just have to be mentally ready for a very tough battle," Sharapova said after squeezing past fellow-Russian Nadia Petrova 7-5, 4-6, 6-4 in her quarter-final on Tuesday.
"Every single point is going to be long and it's just a matter of who wants it more and who is willing to be out there longer."
Sharapova faces fourth seed Kim Clijsters of Belgium in the semi-finals.
"I just felt like there were a lot of ups and downs," said Sharapova, who also beat Petrova in the quarter-finals at Wimbledon.
"You feel like you're playing good, you make great shots, then all of a sudden things don't go right."
"I don't think I was there in the second set. It wasn't the Maria that you usually see on the court, fighting out there, fighting for every single point."
"I was just mentally kind of down and just said, 'Hey, got to get back to work now.'"
Sharapova found the range on her crackling groundstrokes in the third set and led 5-2 before another comeback by Petrova brought her to 4-5 with two game points on her serve to level the set at 5-5.
{{/usCountry}}Sharapova found the range on her crackling groundstrokes in the third set and led 5-2 before another comeback by Petrova brought her to 4-5 with two game points on her serve to level the set at 5-5.
{{/usCountry}}Sharapova, however, forced deuce and claimed victory when a backhand by the ninth seeded Petrova sailed wide.
"It's disappointing," the 23-year-old Petrova said. "The last game I had everything in my hands. I had 40-15 up."
"Suddenly I don't know from where a double fault came. Then I missed an easy backhand and just gave it to her in the rally."
"I feel like if I would get this game, she would be fragile, that I could have won the match," said Petrova.