KEY BISCAYNE, Fla. — Serena Williams toiled for nearly three hours today to reach match point, 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 a slimmer Williams, 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."