Danielle Collins will face Australian Open champion Sofia Kenin in the quarter-finals at Roland Garros after a 6-4, 4-6, 6-4 win over Tunisian 30th seed Ons Jabeur on Tuesday.
World number 57 Collins, a semi-finalist in Melbourne last year, is through to the last eight at a major for the second time.
Collins is one of five unseeded players in the quarter-finals of the women's draw, the most since Grand Slam tournaments were expanded to 32 seeds in 2001.
"I kind of felt like I was in the driver's seat up until 6-4, 3-0, but she's tricky," said Collins, who dropped five straight games as Jabeur fought back in the second set.
"I lost my way there a little bit. I just needed to try and stay positive."
Collins, 26, was a two-time national singles champion at the University of Virginia and turned professional after graduating in 2016 with a degree in media studies.
"I did kind of go an untraditional route and it took me a while to kind of figure everything out," she said. "I'm still trying to figure everything out on this tour."
She lost in the first round of last month's US Open but has since teamed up with former top 10 player and clay specialist Nicolas Almagro, a three-time quarter-finalist in Paris.
"It's a really special treat for me to be able to work with him," said Collins, who beat Kenin in straight sets at Adelaide in January.