Zahlavova Strycova surrendered just four points on her first serve in her 6-0, 6-2 defeat of Swedish qualifier Johanna Larsson.
"I played very good tennis, very solid," Zahlavova Strycova said. "I didn't make many mistakes. I was very focused on my game. Everything was working. I felt very good on the court."
"I won 7-5, 6-0 last time we played," Zahlavova Strycova said. "It was a pretty good match. I was down 5-2 in the first set. She's a very powerful player. I will have to play smart. It's good to be in the semifinals in the last tournament of the season. I will try to do my best."
As for Barthel, she was a 6-3, 6-0 victor over Kiki Bertens, reeling off eight straight games from 4-3 in the first set. Thus, she improved to 7-2 in their head-to-head with her third win in a row against the Dutchwoman.
The surprise of the day saw Czech qualifier Denisa Allertova score a 4-6, 6-3, 7-5 triumph over fifth-seeded Varvara Lepchenko to advance to the semifinals of her first WTA main draw event.
"I started nervously," Allertova said. "But I kept fighting, tried to stay focused and started moving better."
Allertova will next square off with Annika Beck. The German beat Patricia Mayr-Achleitner, 6-2, 6-2, to make her first WTA semifinal since she kicked off her season in Shenzhen. Beck went into this week on a seven-match skid, but is no stranger to success in Luxembourg, having reached her lone WTA final here a year ago.