KEY BISCAYNE, Fla. -- Serena Williams toiled for nearly three hours Thursday to reach match point and then hit two more shots and raised a fist, tired but triumphant.
On a muggy, 85-degree afternoon, Williams' newfound fitness may have made the difference. She overcame a slow start to outlast Svetlana Kuznetsova 3-6, 7-5, 6-3 in the semifinals of the Sony Ericsson Open.
Williams needs one more win for her fifth Key Biscayne title and second in a row.
"I haven't won anything five times, except I win all the time in Uno," Williams said. "I don't think that counts."
She arrived for this year's tournament slimmer, joking after one win that this is the best she has looked since 1982. She was then an infant.
Her recent rigorous training regimen paid off in a semifinal that became a test of stamina.
"I don't feel tired or sore or anything," Williams said 90 minutes after the match. "I feel like I'm really fit. I've been working really hard."
In the final set, Williams broke for a 5-3 lead when she skipped a shot off the net cord, leaving Kuznetsova with an awkward backhand she dumped into the net.
Williams slammed her 12th ace to reach match point, and Kuznetsova then sailed a lob long.
"Serena was a bit fresher," Kuznetsova said. "In the end she was moving well and serving incredibly hard."
Williams' home-court advantage may have been a factor, too. She grew up in nearby Palm Beach Gardens.
"Serena, this is your house," one fan yelled.
Her 46-5 record at Key Biscayne suggests he's right.
"I love playing here," Williams said. "All my friends come out. I promised tickets for Saturday, so I was like, 'I can't lose. I've got to stay in there a little bit longer.' It was mainly my motivation."
Her opponent in the final Saturday will be No. 4-seeded Jelena Jankovic, who beat No. 19 Vera Zvonareva 6-1, 6-4. Jankovic made the final after barely surviving her opening match, when she saved five match points.
Kuznetsova, the 2006 Key Biscayne champion, eliminated three-time champion Venus Williams in the quarterfinals and made a strong bid to complete a sweep of the family.
Serena Williams had a flurry of unforced errors at the start, and she appeared to hurt her back chasing a backhand on the final point of the fourth game. In the next game, Kuznetsova fell behind 0-40 on her serve but then won five consecutive points for a 4-1 lead.
Williams then took an injury timeout and said it later felt as if she had been stuck in the back. A massage from a trainer alleviated the problem.
"Once she came out it got better, like straightaway, and it got even better after that," Williams said.
Her movement and serve appeared hampered for several games but gradually improved, and a 125-mph ace in the second set suggested she felt fine.
With Kuznetsova serving at 5-6 in the second set, Williams broke for the first time since the opening game to even the match. She won the first three points with ferocious groundstrokes, and Kuznetsova blew an easy volley on set point.
Williams won despite 43 unforced errors, and she converted only five of 16 break-point chances.
"I was a little disappointed in the way I played," she said. "But I'm just moving on."
Jankovic barely survived her opening match. In the third set against Sofia Arvidsson, she overcame a 5-1 deficit and then saved five match points in a tiebreak.
"It was a good thing for my confidence to get through the match in that way," Jankovic said. "Playing the way I'm playing now, it's really amazing, so I just hope to continue like this."
She has won every set in her past four matches to reach the final for the first time. Jankovic is 3-2 against Williams, including a victory in their most recent meeting at this year's Australian Open.
"I know how to play against her and know what to expect from her," Jankovic said. "But I also know that I really have to play good tennis in order to win, because she's a great champion and a tough opponent to beat."