PARIS, France - She led, and then trailed, and then led again - but after nearly two hours, Ashleigh Barty booked a spot in the French Open final.

The Aussie ended the dream fortnight of American teenager Amanda Anisimova, 6-7(4), 6-3, 6-3, and will meet another teenager in Czech Marketa Vondrousova with the first Grand Slam singles title for either player on the line on Saturday.

As it happened: Barty holds nerve in rollercoaster semi to book French Open final spot

The No.8 seed nearly fell victim to a comeback from the ages from the American teenager, who lost 16 of the first 17 points and trailed 0-5, 15-40 in the opening set.

"I'm just proud of myself the way I was able to fight and scrap and hang in there and find a way when I kind of threw away that first set," Barty said.

"I played some really good tennis. I played some pretty awful tennis. At the end of the day, I think I was able to scrap and fight and find a way to keep competing. That's probably the best part that came out of today."

Anisimova rallied to win six straight games, but later erased a 4-2 deficit in the ensuing tiebreak, to take a one-set lead, and a string of 17 consecutive points ultimately saw her build a 3-0 lead in the second set. 

However, it was Barty's turn to make a comeback from then on, as she won six straight games to stretch the match to a decider, and she later came from a break down in the final set to seal it. 

"I started off pretty rough. I mean, I was kind of frozen and I couldn't really get into my game. When I was down 5-0, I just tried to keep the ball in the court, and then I went up in that set," Anisimova said.

"I was just trying to do the same thing I was doing, but she just stayed consistent, and it was just really tough. I kind of struggled with her game, so she just outplayed me basically.

"It was just really tough from when I finished the first set. She was playing really well. It was just really tough to win that match."

Barty looked on course to win the last five games of the match, as she held 0-40 on Anisimova's serve in the eighth game, but the teenager made one last stand after nearly two hours of play.

The World No.51 saved five match points total, three on her serve and two more in Barty's ensuing service game, before a perfectly-placed backhand slice down the line sealed the Aussie's spot in the championship match.

"I was 5-Love up in probably all of 15 minutes, I think, and didn't really do a hell of a lot to get to that stage. Amanda gave me some cheapies. I felt I put the ball where I needed to, and then I went away from what was working," Barty added.

"I was really happy the way I was able to respond at a set and 3-Love and to really turn the match on its head, even though it wasn't the best tennis in pretty tough conditions. That's probably what I'm most proud of."

Barty is the first Australian to reach the French Open singles final since compatriot Samantha Stosur made a stunning run to the showpiece match in 2010.

She is also the first woman to reach 30 wins on tour this season, and is assured of cracking the Top 5 in the world rankings no matter the result on Saturday.

Barty will move to World No.3 by reaching the final, which would be the highest ranking by an Australian since Wendy Turnbull ranked in that spot in the week of Jan. 21, 1985.

"Obviously we have seen Sam do so well here numerous times and on many occasions have been at the business end of the tournament," added Barty.

"It's an amazing opportunity for myself and my team. We have worked so hard to put ourselves in these positions. Now, we get to go out there and really enjoy it.

"That's the only way to approach it is to go out and enjoy it, have fun, try and play with freedom. That's ultimately when I play my best tennis and that's what we are after."