Second seed Coco Gauff saw off her fellow American Madison Keys in three sets on Wednesday to reach the semi-finals at the French Open.
Gauff, 21, claimed a see-saw encounter 6-7, 6-4, 6-1 in two hours and 11 minutes.
After coming from a break down in the opener to level at 4-4, Gauff undermined her chances in the tiebreak at six games apiece with two double faults.
Staving off a set point to reach six points-all, Gauff threw in another double fault - her seventh of the set - to furnish Keys with a second set point and the 30-year-old claimed the advantage when a Gauff service return landed in the tramlines.
Gauff regrouped and, assisted by a string of errors off Key's normally reliable forehand, sped into a 4-1 lead in the second set.
But she faltered. A sloppy service game, culminating with a ninth double fault cut the lead to 4-2.
Keys held serve swiftly to ramp up the pressure and racking up mistakes on her own forehand, Gauff dropped and allowed Keys to claw back to 4-4.
But her compatriot was in equally munificent mood. She lost her own service game to give Gauff the chance to serve for the second set at 5-4.
She edged to a set point and levelled the match when a Keys forehand slumped into the net.
Final set quality
A 21-stroke rally started the third set to augur a combat royal.
But Keys cracked. From 2-1, Gauff found her range and confidence to reel off the subsequent four games to progress to the last four the third time in six visits.
"I knew I had to run to keep up with Madison," Gauff told on-court interviewer Mats Wilander.
"It was not an easy match and I'm excited to be in the semi-finals again. I will savour this victory and get ready for the next match."
On Thursday, Gauff will play the unseeded Frenchwoman Lois Boisson. The 22-year-old, who received an invitation to play in the main draw, beat the sixth seed Mirra Andreeva 7-6, 6-3 to become the first Frenchwoman to reach the semi-final since Marion Bartoli in 2011.
