Battling a flu that she’s called the worst illness of her life, No. 1 seed Serena Williams continues her pursuit of a 20th grand slam title when she takes on underdog Lucie Safarova in Saturday’s French Open final at Roland Garros.

After dropping the first set for the fourth time in the tournament, Williams overcame her illness to defeat Timea Bacsinszky 4-6 6-3 6-0 in the semifinals to reach the championship round for the third time in her career.

The 33-year-old could become the third woman in history to claim 20 slam titles, but Williams said after her victory over Bacsinszky that she’s battled her ailment since the early French stages. She even said in a statement that she "kind of collapsed" after the semis, and that she didn't practice Friday, according to ESPN.

"I don't think I've ever been this sick," Williams said. "I didn't expect to win that, I really didn't.

"I got the flu after my third-round match, and I've been really struggling ever since then. Hopefully this is the worst and I'll get better from here.”

Spectators in the stands and those watching at home saw Williams suffer through several coughing fits, and at times she appeared so weakened playing against Bacsinzky that she seemed ready to keel over. But she would persevere.

"I thought, 'If I'm going to lose, I'm going to go for winners.' "

Williams owns a perfect record in the French final, last winning in 2013, but a triumph over Czech Republic star Safarova would allow her to pair her Australian Open title with the French title for the first time in her career.

No. 13 Safarova owns a rough 0-8 all-time mark against Williams, and she’s won only three sets in all of those meetings. But the 28-year-old has yet to lose a single set in this year’s French Open. She’s also been battled tested over five tiebreakers between the first round and the quarterfinals, while upsetting No. 2 Maria Sharapova in the fourth round and No. 7 Ana Ivanovic in the semis 7-5 7-5.

Safarova even fought back from a 2-5 deficit in the first set against Ivanovic before reeling off five straight games.

"It is a dream come true. I cannot believe it," Safarova said to reporters afterwards. "I started slowly but tried to keep up the level and play really aggressively because that was the only way to win."

This is Safarova's deepest run in any grand slam event. In 10 previous appearances at the French Open, she had never advanced further than the fourth round. In 2014, she reached the semifinals of Wimbledon.

Start Time: Saturday, 9 a.m. ET

TV Channel: NBC

Live Online: A live stream is available at NBC Live Extra