Caroline Wozniacki beat American Sloane Stephens 7-6 (8-6) 6-2 on Thursday to reach the semi-finals in New Haven for the sixth consecutive year.
The four-time champion is 23-1 at the Connecticut Tennis Centre, with her lone loss coming a year ago when she had to retire from the semis because of a knee injury.
The former top-ranked player will play Simona Halep after the Romanian beat Russia’s Ekaterina Makarova 6-1 7-6 (8-6).
The other semi-final will feature two players from the Czech Republic. Defending champion Petra Kvitova beat Russia’s Anastasia Pavlyuchenkova 2-6 6-2 7-5.
She will face Klara Zakapalova, who came from a set down to beat Russian Elena Vesnina 4-6 6-0 6-4.