Teenager Mirra Andreeva came from a set down to stun Iga Swiatek and reach the semi-finals of the WTA clay-court tournament in Stuttgart on Friday. 

Andreeva beat the two-time Stuttgart champion 3-6, 6-4, 6-3 and will face either top seed Elena Rybakina or Leylah Fernandez in the semi-finals. 

Swiatek has won four of her six Grand Slams on the French Open clay and was considered among the favourites for the Stuttgart tournament but struggled against the energetic Russian.

The Pole capitalised on some clumsy baseline errors from her opponent to win the opening set but Andreeva converted a crucial break point to take the second set. 

Swiatek ran out to a two-game lead in the deciding set but Andreeva broke back twice to take the initiative, and the match. 

The 18-year-old rising star also eliminated defending champion Jelena Ostapenko in the first round of the tournament. 

Earlier on Friday, Karolina Muchova broke through for a first win over Coco Gauff, eliminating the French Open champion in three sets. 

Muchova had never beaten world number three Gauff in six matches, including a loss in the fourth round of this year's Australian Open, but prevailed 6-3, 5-7, 6-3 to reach the Stuttgart semi-finals for the first time. 

The 12th-ranked Muchova will face Elina Svitolina for a place in the final.

After ensuring Gauff exited the tournament in the quarter-finals for the third straight year, Muchova said she tried not to let the daunting record impact her preparation.

"It was a great fight. I'm just happy that I finally, finally beat her," Muchova said. 

"This was actually our first match on a clay court. On clay we were 0-0 in the matches -- I tried to keep it positive."

Fourth seed Svitolina moved past Czech Linda Noskova 7-6 (7/2), 7-5 to book her semi-final spot. 

The in-form Ukrainian has now reached five semi-finals this season.

Svitolina told reporters she had re-discovered her fighting spirit after a difficult 2025. 

"I had a really difficult end of last year, struggling a bit mentally," Svitolina said. "I think my fighting spirit is back this year. I'm very pleased with that."