No.5 seed Barbora Krejcikova is the highest-seeded player left standing as the Internationaux de Strasbourg reached the semifinal stage on Thursday.

Krejcikova, seeking her first WTA singles title, defeated No.3 seed Ekaterina Alexandrova 7-6(4), 6-1 in a battle between the two highest-ranked players who reached the quarterfinals.

Alexandrova had beaten Krejcikova in all three of their previous meetings, but the Czech turned the tables on the Russian this time around, coming back from a break down in the first set to storm to victory in an hour and 37 minutes.

"I've played her many times, and I always started really bad in the first set, and then she was always improving really, really well," Krejcikova told the press, after her win. "I felt like this time I had to start the first set really well, and I still lost serve and I was still down, but I was closer, and I felt the tiebreak was the deciding point of the match."

Krejcikova was broken at love to cede an early break to Alexandrova, as the Russian routinely fired winners behind Krejcikova to open up a 4-2 lead. But Krejcikova leveled the set at 4-4 after a forehand down the line found the sideline on break point.

The pair moved into the first-set tiebreak, where an ace gave Krejcikova a commanding 4-1 lead. Another solid serve by the Czech was returned wide by Alexandrova to set up triple set point at 6-3, and on her second attempt, Krejcikova closed out the one-set lead after a backhand by Alexandrova flew wide.

Alexandrova held at love to start the second set, but that would be her last bright spot as Krejcikova reeled off six straight games to clinch the victory. Krejcikova won 77 points behind her first serve in the second set to sweep into the semifinals.

"I see that I'm improving every shot, my physical, my mental, everything," Krejcikova said. "I'm just happy that I can actually show it on court and play this high level and play all the top players. It's something that I really like to do, so I'm happy that I'm here."

In the semifinals, Krejcikova will face this week's surprise package, German qualifier Jule Niemeier. The World No.216 notched her first-ever WTA main-draw win in the first round, and then picked up two more wins on Thursday to book a spot in the semifinals.

"I'm surprised, yes, but I'm obviously really happy that I won both matches today," Niemeier told the press after her stirring performance on Thursday. "I'm just really happy with the way I'm playing right now."

"I know what I can play, and what I can do on court, so that I can cause trouble!" Niemeier said with a laugh.

Niemeier finished off a 6-4, 7-6(6) second-round upset of No.7 seed Shelby Rogers in the morning. That match was interrupted by rain on Wednesday with Niemeier leading 6-4, 2-1, but the delay did not hinder the qualifier as she stayed solid in a tight tiebreak to oust the World No.46.

Niemeier upsets Rogers for first Top 50 win, first WTA QF: Strasbourg Highlights

2021 Strasbourg

At the end of the day, Niemeier pulled off a quarterfinal win, storming past 84th-ranked Arantxa Rus, 6-4, 6-1 in 73 minutes. Niemeier was stellar on serve in that match, winning 82 percent of her first-service points and never facing a break point in her clash against the Dutch left-hander.

Niemeier said she learned this week "that I have the level, that I can keep up with all the players. I've beaten two players who are in the Top 100 now, Shelby is in the Top 50. I have the game, and I can beat them."

"I was injured for such a long time in the past, so it was not easy for me," the 21-year-old continued. "I'm just enjoying being on court and playing against really good players."

"I don't feel the pressure because I'm ranked [over] 200 at the moment, so I have nothing to lose," the German added.

The second semifinal will pit No.8 seed Magda Linette against one of 2021's most resurgent players, Sorana Cirstea.

Linette pulled past No.4 seed Yulia Putintseva, 6-3, 6-3 in their 74-minute quarterfinal clash. Linette won 77 percent of her first-service points and broke serve four times to sweep past the two-time Roland Garros quarterfinalist.

The Polish player now finds herself into her first WTA semifinal since her run to the title at Hua Hin in February of last season.

Cirstea, meanwhile, had an unorthodox run into the semis. She defeated No.6 seed Zhang Shuai 6-2, 6-1 in a postponed second-round match this morning.

The winner of that match was guaranteed a spot in the semifinals as prospective quarterfinal opponent Bianca Andreescu withdrew from the tournament after her second-round victory due to an abdominal injury. Cirstea ended up taking advantage of that opportunity, charging past Zhang in exactly one hour.

Cirstea is rising up the WTA ladder again after winning her second career singles title in Istanbul last month -- her first singles title since she triumphed in Tashkent as a teenager in 2008. Cirstea is currently ranked World No.61, 25 spots higher than her 2020 year-end ranking.