PARIS -- Serena Williams, battling the flu, "didn't expect to win" after dropping the first set, but came up with another dramatic comeback to reach the final of the French Open on Thursday.
For the fourth time in the tournament, Williams dropped the opening set and rallied to win. This time, the top seed came back against No. 23 seed Timea Bacsinszky 4-6, 6-3, 6-0 on Court Philippe Chatrier.
"I don't think I've ever been this sick," Williams said after the match. "I didn't expect to win that. I can't believe I won."
Williams said she came down with a flu bug after her third-round match and has been struggling since.
"I haven't been getting better," Williams said. "Hopefully this is the worst and I'll get better from here."
With the temperature nearing 85 degrees on the hottest day of the tournament, Williams walked ever so slowly to changeovers, where even lowering herself to sit down seemed to be difficult. During those breaks, she pressed ice towels against her forehead and neck and guzzled water.
"I tried everything. I thought if I lose, I will lose with a fight," Williams told the crowd in French afterward. "I tried, I tried. I found the energy. I don't know where, but I found it. And I won. I hope that on Saturday, I hope ..."
Cutting herself off, she stepped away from the microphone, bent over and began coughing. She offered a quick wave, then collected her things and left. Off the court, she got a hug from her coach, who then helped her down the stairs toward the locker room.
Williams is 31-1 overall in 2015 and owns a 20-match Grand Slam winning streak, including championships at the US Open in September and the Australian Open in January, raising her total to 19 major singles trophies. Only two tennis players have won more: Margaret Court (24) and Steffi Graf (22).
It was the sixth time in a Grand Slam event this year that Williams dropped the first set. In the previous three years combined, she lost the opening set on only four occasions.
It appeared Williams was in big trouble as Bacsinszky broke the favorite's serve to take a 3-2 lead in the second set. However, Williams broke right back and did not drop another game as part of a 10-game streak to finish the match.
"I really thought I was going to lose, and if I was going to lose, I was going to go for winners," Williams said. "Next thing I know, it was one set-all and I thought, 'I really don't want to play a third set.'
"I was so tired and I just fought for every point and here I am. I don't know how it happened."
Williams has not lost in the semifinals of a Grand Slam event since falling to Kim Clijsters at the 2009 US Open and improved to 24-4 overall in Grand Slam semifinals.
For Safarova, it took a few games longer than she would have liked, but the 13-seed reached her first career Grand Slam final while maintaining her status as the only player in the women's field to not drop a set at Roland Garros this year.
"It's a dream come true, I cannot believe it," said Safarova, who beat two top-10 players for the first time at the same Grand Slam. In addition to the seventh-ranked Ivanovic, Safarova defeated defending champion and world No. 2 Maria Sharapova in the fourth round.
Safarova is the first Czech woman to make it to the French Open final since Hana Mandlikova in 1981.
Safarova trailed 4-1 and 5-2 in the first set before finding her stride and reeling off the next five games. She faltered when serving for the match at 5-4 in the second, though, hitting three double faults -- including one on match point -- before getting broken.
"I started a little slowly, but I tried to keep up the level and tried to play very aggressive because that was the only way to get a win," Safarova said.
Safarova certainly took risks, hitting 36 winners compared to 31 unforced errors.
She was broken in her first service game as she struggled with Ivanovic's deep balls early on. But she broke back in the ninth game with a powerful backhand return. Ivanovic then made some sloppy mistakes, including two double faults as she dropped her serve for the second time, and Safarova converted her first set point.
The left-handed Safarova saved two break points early in the second set, and instead it was Ivanovic who dropped her serve. After Ivanovic leveled at 5-5, the change of momentum did not last. The Serb dropped her serve in the next game, and Safarova kept a cool head to serve out the match.
It was the second consecutive year that Ivanovic fell at the hands of Safarova at the French Open, and the Serbian is now 3-6 all time in their career series.
Not only has Safarova not dropped a set in singles, but she is 10-0 at Roland Garros if you include what she's done in doubles. She and partner Bethanie Mattek-Sands will play in the women's semifinals Friday.
The Associated Press contributed to this report.