ST. PETERSBURG, Russia (AP) — Simona Halep withdrew from the St. Petersburg Ladies Trophy on Friday because of a knee injury, the same issue that she blamed for her opening-round loss at the Australian Open.

The fourth-ranked Romanian had said she was pain-free after her win over Ana Konjuh this week.

Halep was the top-seeded player in St. Petersburg. Her withdrawal sends Russian wild-card entry Natalia Vikhlyantseva into the semifinals, matching her best showing at a WTA tournament.

Vikhlyantseva, ranked 115th in the world, will next play either defending champion Roberta Vinci or Kristina Mladenovic.

Also, second-seeded Dominika Cibulkova advanced by beating fifth-seeded Elena Vesnina 6-3, 6-3. The Slovak will next face either Svetlana Kuznetsova or Yulia Putintseva.