Flavia Pennetta rallied for a 6-2, 4-6, 6-3 semifinal victory in the LA Women's Tennis Championships on Saturday night, with Sharapova committing 61 unforced errors against the Italian.
"I didn't feel physically fresh from the beginning of the match," Sharapova said. "I was surprised it actually went to the third. I had my opportunities, I just couldn't close it out."
Sharapova blew a 3-1 lead in the third set, dropping her final three service games as she continued to struggle with her serve in her sixth tournament since returning in May.
"Am I happy with where it is? Absolutely not," she said. "I feel like there's more work to be done. There's nothing that a basket of balls can't achieve."
Sharapova said she wore tape on her right shoulder for the first time this week because it needed support.
The 22-year-old Russian was off the WTA Tour for nearly 10 months, including surgery in October, before returning in May. She came into the week ranked 61st, which meant she didn't receive a first-round bye, and hasn't won a title since April 2008.
She reached the quarterfinals last week at Stanford, losing to Venus Williams in straight sets.
"This is still a work in progress," she said. "I'd definitely like to forget I was gone a long time but sometimes you got to put things in perspective."
Sharapova had 16 double faults, including one that set up Pennetta's second match point. Sharapova sent a forehand wide to lose the match and drop to 9-2 in three-set matches this year.
Pennetta advanced to Sunday's final against Australian Samantha Stosur, who routed Sorana Cirstea 6-3, 6-2. Pennetta lost to Dinara Safina in last year's title match.
Sharapova was wildly inconsistent throughout the match, hitting 34 winners to Pennetta's 17. She faced break points in every service game in the third, and only staved them off once in the third game, smacking an ace down the middle to take a 2-1 lead. She broke Pennetta in the next game before the Italian took control for good.
"I was 3-1 down and I was thinking it was over, but I just tried to fight," Pennetta said. "It was a little bit difficult for me. I started to feel a little pressure. She's a great champion, it was not easy to beat her."
On the changeover between the first and second sets, Sharapova's coach, Michael Joyce, came on court and told her she had to be more aggressive because Pennetta was keeping a lot of balls in play.
Later in the match, Joyce told Sharapova that "this girl can fall apart" only to see Pennetta break serve in the next game.
"The serve was a problem for both," Pennetta said. "I was very nervous with my serve because she was returning so well. She started to make a lot of mistakes."
Stosur is making a rare appearance in a singles final. Her greatest success has come with a partner, having won 22 career titles, achieved the No. 1 doubles ranking and earned two Grand Slam mixed titles.
She's enjoying a strong start to the summer hardcourt season, reaching the Carson final a week after her semifinal finish that included a three-set win over Serena Williams at Stanford.
"My whole career I've been trying to get to this point," Stosur said. "It kind of looks like I've done it late, but I don't worry too much about that. I took a little longer to develop."
Stosur has lost in four career singles finals, including one last year in Seoul. A victory Sunday could boost the Aussie into the top 15 for the first time from her current ranking of 19th.
"The last one in Seoul, I got a little bit ahead of myself," she said. "Since then I've gotten a lot better at closing out matches. If I can handle it right, there's no reason I can't do it.
"I've just got to treat it like I have the last four matches here and don't think of it like a final."
Stosur lost just four points on her serve in the first set, dominating with three love games. She earned the only break in the second game, also the only one that went to deuce.
"I was putting balls in places she didn't really want to move to," she said. "Maybe she wasn't moving as best she can, but I made it hard on her. I kept pressure on her the whole match."
The Aussie won 81 percent of her total service points in the 62-minute match.
Stosur served three of her seven aces in the second game of the second set. She then led 2-1 after breaking Cirstea, who committed 25 unforced errors in the match. She went up 4-1 with another service break and closed out the match when Cirstea pulled a backhand service return wide.
Cirstea, a 19-year-old Romanian, was bothered by pain from plantar fasciitis in her right foot, the same problem she had Friday un a three-set win over Agnieszka Radwanska.
"It was bothering me," she said. "She was in good form and if I wanted to beat her I had to be 100 percent. Sam was playing so good, she didn't give me any chances."
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