Pegula stuns tearful Swiatek as US take charge of United Cup
Less than two weeks before the Australian Open, Swiatek had no answers to the American's powerful serve and searing returns, crashing 6-2, 6-2 in a deflating 71-minute defeat in Sydney.
"I played her a lot in a lot of different conditions but I felt these were definitely the fastest conditions," said Pegula, ranked three in the world.
"I thought I did a really good job playing aggressive, serving smart and returning really well."
Men's world number 19 Tiafoe then put the United States on the cusp of Sunday's final when he swept past Kacper Zuk 6-3, 6-3. Tiafoe was initially supposed to play Daniel Michalski, but he pulled out with illness.
With the roof closed at Ken Rosewall Arena on a rainy day in Sydney, Swiatek lost the opening seven points to be broken and go 40-0 down in the next game.
She woke up to level at 1-1, but lost focus again and was broken twice more to concede the first set in 39 minutes.
Another early break for Pegula in the second set put Swiatek on the back foot again and she had no way back against a player in scintillating form.
It was a massive blow for Swiatek ahead of the Australian Open after coming into the match as favourite following a dominant 2022 in which she beat Pegula four times, including at the French and US Opens that she went on to win.
Tiafoe was also in top form, making a quick start and never looking back.
Although Zuk provided some resistance, especially early in the second set, he was unable to stop the charging American, who is now a combined 7-0 in singles and mixed doubles at the tournament.
"My level is pretty high, it has been for a while now," said Tiafoe. "I believe I'm playing some of the best tennis of my life, I'm just having fun out there on court.
"Jess (Pegula) is an unbelievable player and after that I was like, 'yeah, I need to come out and put on a show for you guys'."
The tie's final two singles matches - Taylor Fritz v Hubert Hurkacz and Madison Keys v Magda Linette - are on Saturday ahead of a mixed doubles rubber, if required.
The teams tournament began with 18 countries but has been whittled down to four after round-robin ties over six days in Perth, Brisbane and Sydney.
Poland, USA and Greece all progressed to the last four as city winners, along with "lucky losers" Italy.
Greece, spearheaded by top-10 players Stefanos Tsitsipas and Maria Sakkari, face an Italian team led by Matteo Berrettini and Martina Trevisan on Friday evening.
