World number one Ash Barty has been knocked out of the Charleston Open after a straight-sets loss to unseeded Spaniard Paula Badosa in Friday's quarter-finals. (More Tennis News)
Badosa won 6-4 6-3 over the favoured Australian in one hour, 16 minutes to book a spot in the last four on the green clay and a meeting with 15th seed Veronika Kudermetova.
Kudermetova beat 2017 US Open winner Sloane Stephens 6-3 6-4 in her first win over a grand slam winner.
Former French Open junior champion Badosa, who beat fifth seed Belinda Bencic in the second round, claimed her second career victory over a top-20 player against Barty.
Barty may have hit 34 to 19 winners but she also made twice as many unforced errors, 24 to 12.
The Spaniard broke Barty's serve five times while she sent down seven aces and saved 12 of 14 break points.
"I was quite nervous today but I think I served very well and I think that was the key for the match," Badosa said in her on-court interview.
"It was a tough match but I was there until the last moment and I managed to win."
World number 71 Badosa becomes the lowest-ranked player to beat Barty since September 2019.
The Australian had won eight matches in a row after last week's triumph at the Miami Open.
Unseeded Montenegrin Danka Kovinic came from a set down to topple 11th seed Yulia Putintseva 6-7 (2-7) 7-5 6-1.
Kovinic, who knocked out Petra Kvitova in the third round, will play 12th seed Ons Jabeur in the semi-finals after she overcame Coco Gauff 6-3 6-3.
Meanwhile, at the Copa Colsanitas in Bogota, fifth Tamara Zidansek beat Italy's Sara Errani 6-3 6-4 to claim a spot in the semi-finals.
Viktoriya Tomova outlasted qualifier Nuria Parrizas-Diaz 5-7 6-2 6-4 in almost two and a half hours, while Harmony Tan and local wildcard Maria Camila Osorio Serrano also won.