SYDNEY - The United States, Poland and Greece won their city finals on Wednesday to reach the semifinals of the inaugural United Cup, while Italy completed the Final Four as the best-performing runner-up.

The semifinals will be played from Friday to Saturday at Sydney's Ken Rosewall Arena, where the United States will play Poland and the event's top seed Greece will take on Italy.

Emerging as the first qualifier for the semifinals, the United States sealed a 4-1 victory over Britain when Jessica Pegula and Taylor Fritz overcame Harriet Dart and Daniel Evans 6-4, 6-4 in a 72-minute clash.

Earlier, world No. 11 Madison Keys opened the Sydney City Final with a 2-6, 6-3, 6-4 victory over Britain's Katie Swan. Cameron Norrie leveled the tie by upsetting Fritz 4-6, 7-5, 6-4, but world No. 3 Pegula's comfortable 6-2, 6-0 win over Dart tipped the scales in favor of the US.

World No. 19 Frances Tiafoe downed world No. 27 Evans 3-6, 7-5, 6-3 in the men's singles, giving the United States a decisive 3-1 lead.

The Ken Rosewall Arena in Sydney saw the United States compile nine wins out of 10 matches throughout the round-robin stage, top the group standings and advance to the semifinals with the largest winning margin.

"Obviously I felt great today, but every day is a different day, so we will see. I feel good going into the semis for sure," Pegula said at the post-match press conference.

Walking onto court in Perth's RAC Arena with Greece trailing 0-1, world No.4 Stefanos Tsitsipas clawed his way to a vital 6-0, 6-7 (4), 7-5 victory in a two-hour, 30-minute encounter against his Croatian opponent Borna Coric, who had prevailed 3-1 in their previous head-to-head series.

"My fighting spirit was lit up. I was there. I was using my footwork very well. I was precise, and that gave me the win," said the 24-year-old Greek.

In the night session, Tsitsipas came back onto court and teamed up with Maria Sakkari in the mixed doubles, as Greece and Croatia were dragged into a deciding clash with the tie locked at 2-2.

The Greece pair finished the Perth City Final with a 7-6 (6), 6-4 triumph over Croatia's Coric and Donna Vekic.

A 2-2 draw also occured at the Pat Rafter Arena in Brisbane, with Poland finally earning the city championship after world No. 1 Iga Swiatek and No. 10 Hubert Hurkacz beating the lower-ranked Italian pair of Camilla Rosatello and Lorenzo Musetti 6-1, 6-2.

The loss didn't see Italy bow out from the United Cup stage, as a record of 10 match wins and five defeats helped the team progress to the Final Four as the best runner-up.