SYDNEY, Australia -- Jessica Pegula scored her first win over a reigning World No.1 in the first rubber of the United Cup semifinals, racing past Iga Swiatek 6-2, 6-2 in 71 minutes. Frances Tiafoe then gave the United States a 2-0 lead with a 6-3, 6-3 win against Poland's Kacper Zuk.

If the Americans can win one more match Saturday, they will face either Italy or Greece. After Day 1, the Italians are up 2-0 in the best-of-five showdown. 

Pegula's previous career-best win by ranking had come against then-ranked No.2 Naomi Osaka in the second round of Rome 2021. Pegula had lost to Swiatek in all four of their 2022 encounters. 

Swiatek was slow out of the blocks, losing the first seven points of the match -- five with forehand errors. A slew of terrific winners enabled her to break Pegula back from 40-0, but it was the American who maintained her initial momentum.

Pegula, 28, seemed thoroughly at home on a court she has competed on throughout the United Cup's group stages. She teed off repeatedly on Swiatek's serves, firing three clean return winners for a 4-1 lead. Pegula outrallied Swiatek in baseline exchanges, ultimately tallying 21 winners to her opponent's 18.

Trevisan upsets Sakkari in three-hour United Cup semifinal; Italy up 2-0

In the first set, Pegula won 15 of her first 18 return points. In the second, she lost only five points behind her serve and did not face a break point.

"[The] conditions are totally different than anywhere else I've played her," Pegula said afterward. "Obviously maybe I had a little bit of an advantage, they just flew in yesterday. Definitely the fastest conditions I have played here.

"Every other place I've played her has been pretty slow. I think that favored me a lot, and I was able to use that to my advantage and play a really super clean match. I think I just was able to execute my game plan probably better than I have previous times."

With an advantage in hand, Tiafoe, 24, played with confidence in a 6-3, 6-3 victory against Poland's Zuk, who replaced Daniel Michalski (illness) in 1 hour and 20 minutes.

Tiafoe saved all five break points he faced inside Ken Rosewall Arena.

Tiafoe has won all four of his matches at the inaugural United Cup, losing only one set.

The United States' No.1 men's singles player, ATP No.9 Taylor Fritz, will have an opportunity to close out the tie Saturday morning when he takes on No.10 Hubert Hurkacz. If he does not, WTA No.11 Madison Keys can do so in the second Saturday match, when she faces No.48 Magda Linette.

It's not over yet

The Fritz/Hurkacz and Keys/Linette head-to-heads are both tied at 1-1, with both of Keys and Linette's encounters coming in the past two months. Following her loss, Swiatek expressed faith in her compatriots to pull off a comeback.

"I have a belief that we can do a lot," she said. "Magda played really solid match two days ago, so I hope she's going to be confident. I would say they are both 50/50, but it depends. I will do my best on the bench. I wasn't able to do that on court today, but I will do my best to cheer and help them."

Pegula and Tiafoe are backing their compatriots.

"Taylor and Hubi is going to be tough," Tiafoe said. "I think whoever serves better is probably going to get over the line. I'm going to back Taylor's serve tomorrow, obviously. They haven't played a proper match in a while. They're both in two different stages of their career. They're both playing the best tennis of their life. So we'll see."

Pegula had similar belief in Keys.

"Madi and Magda is going to be tough," she said. "Obviously, again, they haven't been here very long; hopefully we can use the courts to our advantage a little bit. Yeah, I gotta back Madi with her big game, as long as she serves pretty well. She's been playing some really solid tennis. I think it helps she kind of got that tough three-setter [against Katie Swan] out of the way, so hopefully she'll feel pretty loose tomorrow.

"2-0, it's nice, but sometimes it's tough to close it out as well."