CHARLESTON, SC, USA -- No.12 seed Kiki Bertens of the Netherlands filled out the final four at the Volvo Car Open on Friday night after a straight-set quarterfinal victory over No.14 seed Alizé Cornet of France, 6-2, 7-5.

Bertens, a semifinalist at Roland Garros in 2016, told the press afterwards that "the clay is helping me a little bit, like with my forehand and with my heavy strokes, but I guess it's more mentally. My level is maybe 20 percent better, but in my head I feel like I'm 80 percent better."

The Dutchwoman has yet to drop a set this week, and continued her fine form with the 98-minute win over Cornet. Bertens came into the match having lost three of her previous four meetings with the French player, but moved past Cornet to reach her first semifinal of 2018.

The twelfth seed broke Cornet seven times in the match, and had 21 winners, compared to the Frenchwoman's 12. Cornet was perfect on break points, going 4-for-4, but only held three times in 10 service games, and committed 33 unforced errors.

Bertens will take on No.7 seed Madison Keys in the semifinals, after the American survived a three-set tussle with her compatriot Bernarda Pera in an earlier quarterfinal encounter on Friday.

"It's going to be a tough match," said Bertens. "[Keys is] hitting the ball so hard. I have to defend a lot, and play aggressive where I can, and then we'll see how that goes. But right now I'm just really happy to be in the semis, and hopefully I can play a great match tomorrow."

Cornet had a tough start to the match, considering she was a day removed from a three-set victory over top seed and World No.7 Caroline Garcia, the 16th Top 10 win of her long career. The Frenchwoman dropped her first two service games of the tilt, and Bertens held for 3-1 to begin to pull away.

Bertens dropped half of her service games in the set, but started to take command in all of Cornet's service games behind her vaunted heavy forehand, which serves her exceptionally well on clay courts. Cornet was misfiring on her backhand by the end of the set, allowing Bertens to take the opener 6-2. Cornet only had one winner in the set, and never held serve.

For the second consecutive time in the match, an exchange of breaks opened a set, but Cornet finally held her serve in the third game, to lead 2-1. The advantage was short-lived, though, as a forehand error by the Frenchwoman in her next service game gave Bertens a lead at 3-2.

Bertens served for the match at 5-4, but struggled with a hip injury in that game, having just received treatment during the previous changeover. Cornet utilized the Dutchwoman's cautious movement in that game, and broke for 5-5.

Bertens was unfazed by neither the break of service nor the injury, and broke straight back behind more deep hitting, setting up a second chance to serve out the match at 6-5. This time, the Dutch No.1 closed it out, finishing off the match by chasing down a Cornet drop shot and returning it crosscourt for an ingenious winner.

"The treatment was good," said Bertens. "It got locked a little bit, so I needed the trainer to just release it a little bit, and of course, I was still a little bit struggling after that, but I'm just going to recover now and go back in again and hopefully it will be fine for tomorrow."