KEY BISCAYNE, Fla. -- Jennifer Capriati is in a more mellow mood these days, not stressing out about bad calls, double faults or even the Williams sisters.

Her new attitude will be put to the test Saturday, when Capriati bids for a breakthrough victory against top-ranked Serena Williams in the final of the Nasdaq-100 Open.

Capriati is 0-4 against Venus Williams and has lost six matches in a row to Serena, all of them close. This time, Capriati will play on her 27th birthday against Serena, who is 16-0 this year.

"Maybe she'll feel generous and give me a birthday present and let me win,'' Capriati said with a laugh. "I figure one of these times it has got to go my way.''

In 11 tries, she has never won the Key Biscayne title, but by beating Chanda Rubin 6-2, 6-4 on Friday, Capriati earned a berth in the final for the third year in a row. She lost to Venus in 2001 and to Serena in 2002.

Also in action again Saturday will be No. 2-seeded Andre Agassi, who plays No. 9 Albert Costa in the men's semifinals. Agassi, bidding for a sixth Key Biscayne title, advanced by playing almost flawless tennis to beat No. 19 Younes El Aynaoui 7-6 (6), 4-6, 6-1.

Costa won his rain-delayed quarterfinal match, taking 13 minutes to finish off No. 4 Roger Federer 7-6 (4), 4-6, 7-6 (7). The match was suspended Thursday in the final game of the final set, then resumed 19 hours later.

Costa overcame three match points, including one in the final tiebreaker.

"Today was like heads or tails,'' said Costa, who owns 12 career titles but is bidding for his first hard-court championship.

Fellow Spaniard Carlos Moya, seeded fifth, earned a berth in the final by winning the final five games to beat No. 13 Paradorn Srichaphan 6-4, 6-2.

Capriati, seeded sixth, has won plaudits at Key Biscayne not only for her inspired play but for her blissful demeanor. She beamed as she toweled off in her changeover chair after beating Rubin.

"It's a beautiful day to play tennis,'' she told a TV interviewer. "We're here. We're happy. We're alive. How much better can it get?''

Crankiness has accompanied Capriati's inconsistent results in the past year. Her tantrum during one match prompted a sponsor to pull out of a $1.8 million endorsement deal.

But at Key Biscayne she has yet to cause a fuss, and she has been positively pleasant during interview sessions that were often tense in the past.

"I just see no point in just stressing myself out for no reason,'' she said.

Perhaps it's because of her birthday. Or perhaps it's because her younger brother, Steven, is working as her hitting partner, and easing the strain on her relationship with their feisty father, Stefano.

"It's a combination of some things, making some changes on the outside and then also on the inside,'' she said. "I mean, I'm getting older, so it's like, `How do I want to live my life? Do I want to be stressed out and take for granted everything that I'm doing? Or do I just want to enjoy the time that I have now while I'm doing it?'''

Capriati didn't make a direct reference to her father. But when asked if maturity was the reason she has become more laid back, she responded: "You could say that. But I know a lot of, like, 50-year-olds who don't do that.''

There was little stress in the semifinal for Capriati, who easily won the match postponed one day because of rain. She lost serve in the opening game but dominated after that, smacking 27 winners and breaking Rubin's serve in six of nine games.

Rubin, who was seeded 12th, said the Capriati-Williams final will be worth watching.

"You'd like to give the edge to Serena,'' Rubin said. "She's confident and hasn't lost a match this year, and Jennifer hasn't beaten her the last few times they've played, even though they've been some tough matches.

"But you never know.''