just the second for Wozniacki, from Denmark, in 25 career matches in New Haven, where she is a four-time champion. Her only other defeat came a year ago when she was forced to retire from the semifinals because of a knee injury.
Halep will play defending champion Petra Kvitova of the Czech Republic, who beat countrywoman Klara Zakopalova 6-0, 6-1 earlier Friday for her eighth consecutive victory at New Haven.
Kvitova, who had fought through three, three-set matches en route to the semifinals, dominated her friend in a meeting that lasted only 50 minutes.
"I played my game, finally today," she said. "I played aggressively. I can improve my serve. I had some double faults again, so I can still improve."
That might be hard for Zakopalova to believe. Kvitova won 53 of the 76 points in the match.
Zakopalova earned only three points in the second set before holding serve and closing to 5-1 with her only game win. She finished with 10 points in the set.
Kvitova ended things on her serve, striking an ace on the final point.
"She just played fantastic tennis today without any mistakes," Zakopalova said. "I think everything was working for her, so I have to just congratulate her, wish her good luck because she was the better player today, for sure."
Kvitova leads the WTA Tour's top 100 players with 29 three-set matches this season. She didn't let this one get close, with each set lasting 25 minutes.
"That's helpful, for sure, before (Saturday's) final," she said. "I hope that helps me to have more time for rest, not be on the court pretty long. So that's the good thing."
The 31-year-old Zakopalova has not beaten a top-10 player since 2011, but goes into the U.S. Open seeded No. 31. She upset eighth-seeded Dominika Cibulkova, and beat Monica Puig and Elena Vesnina before losing to Kvitova.
"I have to forget this match because it doesn't matter who is on the other side," she said. "So it gives me a lot of confidence, this tournament, for sure. I played a great three matches. I hope it's going to work for me in the US Open."
Kvitova, ranked No. 9 in the world, will face the winner of Friday night's second semifinal between four-time New Haven champion Caroline Wozniacki and Romanian Simona Halep.
Wozniacki is 23-1 in New Haven. Her only loss came last year when she had to retire from a semifinal match against Russia's Maria Kirilenko, who lost to Kvitova in the final.
Kvitova, the 2011 Wimbledon champion, has never won the same tournament in consecutive years. She would like to add that feat to an already impressive resume.
"I have one more new motivation then," she said.