Petra Kvitova returned to the French Open semi-finals for the first time in eight years on Wednesday after defeating Germany's Laura Siegemund 6-3, 6-3, describing Roland Garros as her "lucky place".

Czech seventh seed Kvitova, a two-time Wimbledon champion, will now face Australian Open winner Sofia Kenin who knocked out fellow American Danielle Collins 6-4, 4-6, 6-0 for a place in Saturday's final.

"It means a lot to be back in the semi-finals," said 30-year-old Kvitova who was beaten by eventual champion Maria Sharapova when she made the same stage in 2012.

"After my last match, I was very emotional to be in the quarter-finals. Now I am in the semis. I never imagined this would happen after everything that has happened.

"This is my lucky place."

It was Paris where Kvitova made her comeback in 2017 after spending six months recovering from a terrifying knife attack at her home in December 2016.

Petra Kvitova celebrates victory over Laura Siegemund
Petra Kvitova celebrates victory over Laura Siegemund AFP / Anne-Christine POUJOULAT

The frenzied assault required a four-hour operation and left her with damaged ligaments in her playing hand. Doctors warned her that her career may be finished.

On Wednesday, Kvitova fired 22 winners and six aces past 32-year-old Siegemund, the world number 66 who was playing in the quarter-finals of a Slam for the first time.

One break of serve in the opener was enough for Kvitova while five more breaks followed in the second set.

Kvitova, who has yet to drop a set at the tournament, claimed victory when Siegemund served up a third double fault of the tie.

"I am happy to be here and to be able to compete with the best especially in these conditions -- roof open, roof closed, sunshine, windy."

Fourth three-set win for Sofia Kenin
Fourth three-set win for Sofia Kenin AFP / Thomas SAMSON

Siegemund leaves behind a tournament to remember having been accused of hitting the ball on a double bounce in her first round win over Kristina Mladenovic.

She then munched on a plate of food courtside during her fourth round victory against Paula Badosa.

On Wednesday, she signed off with a time violation for taking too long between points.

"I was on the line, I was bouncing, I was starting my movement, and it was about once, and literally she (the umpire) was saying that it was one second too slow. I mean, that's a joke," said Siegemund.

Fourth seed Kenin moved two wins from a second Grand Slam title of 2020 when she defeated Collins on the back of 38 winners, out-hitting her 26-year-old rival who had arrived in the last eight having unleashed a tournament total of 140.

It was Kenin's fourth three-set win at the tournament.

"It's really special to be in the semi-finals for the first time. I'm super happy," said Kenin.

Collins, who had knocked out 2016 champion Garbine Muguruza in the third round, required a medical timeout off-court on an abdominal injury at 4-0 down in the decider, but Kenin's resolve never wavered.

Former college tennis champion Collins endured a roller-coaster of an afternoon with one US network claiming she ordered her boyfriend, Aussie Rules player Tom Couch to move to another seat while winning points were accompanied by high-pitched screams of "come on".

"I had my boyfriend move to a different spot because I was distracted by something in front of him. I just wanted to be able to look at him from a different location," explained Collins.

"Sometimes too when I was serving the ball, I could see my team in the background, and I didn't like that. Actually during the Muguruza match they sat on the side of the court, and then I really didn't like when they were sitting behind the court when I was playing Ons Jabeur (in the last 16)."

Kenin, diplomatically, insisted she did not notice the noise from the other side of the net.

"I try not to focus on what's going on around me. I just try to focus on myself and just block everything out," she said.