SYDNEY, Australia -- World No.3 Jessica Pegula and No.11 Madison Keys gave the United States an early 2-1 lead over Great Britain, and Frances Tiafoe clinched the win for the Americans. 

With the Sydney City Final secured, the U.S. moves on to the semifinals of the United Cup, which will begin Friday, also in Sydney. The Americans will face Poland. 

Keys gave Team USA an early 1-0 lead after rallying from a set down to defeat No.145 Katie Swan 2-6, 6-3, 6-4.

Later, No.14 Cameron Norrie put Great Britain on the board with a clutch 6-4, 5-7, 6-4 win over No.9 Taylor Fritz.

Hot Shot: Pegula Shows Good Hands In Sydney

But a comprehensive 57-minute masterclass from Pegula, who beat Harriet Dart 6-2, 6-0 gave the Americans the lead again before Tiafoe gave his team the insurmountable lead.  

Tiafoe rallied past Daniel Evans 3-6, 7-5, 6-3 and has won all three matches he has played this season.

From the start of the day, this was an impressive performance by the Americans. 

"I think Madi really set the tone with her match," Pegula said. "I think I did everything really well today. I could feel it. Some days you come out firing and you feel really good. I was honestly trying to settle myself down because I was seeing the ball really well today."

Great Britain had tallied upset wins against Australia and Spain in group play. Swan looked keen to continue the trend early, as she jumped on a slow-starting Keys to take the opening set. 

The big-serving American bounced back quickly to take the second set but could not hold on to an early lead in the decider. Swan broke back to 3-3 in the third set off a shaky double fault from the American, and it appeared as though Tim Henman's squad had regained the momentum for good. 

But Keys showed her experience in the end. She played a disciplined and patient return game to break Swan one final time to 5-4 and coolly served out the win after 2 hours and 18 minutes. 

The pressure was on Norrie, and the World No.14 was not fazed, playing consistently from the baseline to move past Fritz after 2 hours and 15 minutes on Ken Rosewall Arena.

With the pressure on Tiafoe. he showcased his all-court game. The World No. 19 timed his forehand cleanly to pull Evans around and he looked comfortable moving forward, clinically finishing points at the net on Ken Rosewall Arena.

Late Wednesday, Pegula teamed with Fritz to knock off Dart and Evans in a dead rubber to give the U.S. a 4-1 win. 

The ATP Tour contributed to this report.