Serena Williams survived another scare at the French Open as the American battled back from a set down to beat Timea Bacsinszky and secure her place in the final.
Williams has now come from a set down to win four times at this tournament, trumping her previous grand slam record of three, as the top seed showed her relentless fighting spirit again to win 4-6 6-3 6-0.
The world number one will now play Czech Lucie Safarova in the final as she bids to win her third title at Roland Garros and 20th overall.
Williams was visibly under the weather throughout the match on the Philippe Chatrier court, coughing and spluttering in between points, but, as so often in her career, she found a way through.
"I thought I had lost but I found some energy and I won," Williams said. "I hope I get better for Saturday. I feel ill."
Williams also had to contend with a brilliant display from Bacsinszky, who almost gave up tennis two years ago when she began an internship in hotel management to work in restaurants.
It was Bacsinszky's first appearance in a grand slam semi-final, but the Swiss showed no signs of nerves early on, serving an ace to hold her first service game.
She more than held her own in the rallies too, taking Williams' ground-shots as early as possible and pinning the American back with a number of driving double handed backhands.
Bacsinszky's strong start was rewarded in the fifth game as a brilliant drop-shot and lob opened up a second break point, which she converted with another backhand winner to lead 3-2.
Williams' illness looked to be causing her more discomfort by the game and the number one seed, breathing heavily, took every change of ends to smother her head with ice towels.
It proved no distraction for Bacsinszky, however, whose relentless hitting at the back and clever angles at the front made Williams appear all the more sluggish and the Swiss served for the set at 5-4.
Two set points were saved by the American but a forehand winner gave Bacsinszky a third opportunity, and this time she closed out.
Williams dug deep at the start of the second set but neither her illness nor Bacsinszky would let up and the Swiss clinched a break point, the last of six in the fifth game, to lead 3-2.
The world number one came storming back, however, as Bacsinszky's faultless hitting began to show cracks and Williams won four games in a row to force a decider.
The momentum was now firmly in the top seed's favour and two missed forehands from Bacsinszky, both with the court at her mercy, gave Williams an immediate break.
The 19-time grand slam champion then clicked into gear, winning the next five games in a row with some blistering tennis, to seal a gutsy victory in one hour and 54 minutes.
Williams will play Safarova in the decider on Saturday after the Czech beat Serbian Ana Ivanovic 7-5 7-5 to go through to her first grand slam final.
Safarova has previously played only one major semi-final, when she lost at Wimbledon last year, but the world number 13 overcame early nerves to defeat Ivanovic.
The win represents another major scalp at Roland Garros for Safarova, who knocked out second seed Maria Sharapova in the last 16.
"It's a dream come true, I still cannot believe it," Safarova said. "I started a little slowly today but I tried to keep up the level and started to play really aggressive because that was only the way to win. It's unbelievable."
Ivanovic came into the match on the crest of a wave after reaching her first semi-final since winning her sole grand slam title in Paris seven years ago.
The Serbian made her confidence count in the early exchanges as she dominated Safarova with a powerful forehand from the back and raced into a 4-1 lead.
Safarova was struggling to find a foothold in the contest but was handed a lifeline in a lengthy sixth game when Ivanovic had two break points to go 5-1 ahead but spurned both and allowed Safarova to hold for 4-2.
It proved to be a pivotal moment in the contest as Safarova sparked into life, driving her whipped forehand into the corners and breaking back to level at 5-5.
The fightback seemed to melt the confidence of Ivanovic, whose own forehand began to go awry and whose serve started to crumble under the pressure.
Two double faults gifted Safarova another break for 6-5 before a snatched volley into the net helped the Czech hold to love and clinch the first set.
Ivanovic regained her composure at the start of the second but she could not halt the momentum of Safarova, who claimed her eighth game out of nine to go 3-1 up.
A brilliant backhand from Ivanovic reduced the deficit to one but she was unable to break and Safarova served for the match at 5-4.
With the end in sight, Safarova suddenly lost her nerve as she served three double faults, including one on match point, to give Ivanovic a gutsy break but the Serb failed to consolidate and Safarova was again one service game away.
This time she made no mistake, serving out her third match point to complete a superb victory in one hour and 52 minutes.
