The 30-year-old seventh seed, a two-times champion at Wimbledon, reached the last-four stage on the clay courts at Roland Garros for the second time since 2012 and has yet to lose a set at this year's tournament in Paris.

Siegemund, ranked 66th in the world, did not pose a challenge in the opening set but gave a good account of herself in the second despite suffering a lower-back problem midway through the set.

Kvitova converted her second match point when her 32-year-old opponent served a double fault.

The Czech will meet the winner of the all-American clash between Danielle Collins and Australian Open champion Sofia Kenin for a place in the final.

Nadia Podoroska has already won more matches at this French Open - eight - than it usually takes to raise the trophy.

That is because the 131st-ranked Argentine has come all the way from qualifying to reach the semi-finals, becoming the first woman to achieve that feat at Roland Garros in the Open era.

Having never won a main-draw grand slam match before last week, the 23-year-old could hardly believe it after her 6-2 6-4 quarter-final victory over third-seeded Elina Svitolina on Court Philippe Chatrier.

Asked afterward whether she is pinching herself to make sure it's not a dream, Podoroska replied: "No. I don't want to wake up."

Podoroska is only the third female qualifier to get to the semis at any major tournament in the Open era, which began in 1968, and the first since Alexandra Stevenson at Wimbledon in 1999.

Another qualifier in Martina Trevisan had a chance to join that list later on Tuesday but could not quite take the last step. The 159th-ranked Italian, who also had not won a main-draw grand slam match before this tournament, lost 6-3 6-1 to unseeded Pole Iga Swiatek.

"I'm sad for the match, but it's an incredible two weeks for me," said Trevisan, who dropped tennis for more than four years and returned to the sport in 2014.

Australian Associated Press