The encounter between both last year's quarterfinalists was a highly anticipated one but it was Pegula who prevailed over the 2021 Roland Garros champion after a match that lasted one hour and 41 minutes
In the pre-quarters, Swiatek will take on last season's Wimbledon champion Elena Rybakina of Kazakhstan, who defeated the previous year's runners-up Danielle Collins 6-2, 5-7, 6-2 in their third-round match-up
Gauff won the match by a comfortable margin of 6-4, 7-6(4). She will be facing Bernarda Pera in her next, with the winner of the clash advancing to the pre-quarters stage of the tournament.
Fritz was followed by Madison Keys, who defeated Magda Linette 6-4, 6-2. Fritz and Pegula then completed a 5-0 sweep by defeating Lukasz Kubot and Alicja Rosolska in mixed doubles, 6-7(5), 6-4, 10-6. The US team is now 4-0 in mixed doubles in the United Cup.
The USA will complete Group C unbeaten after having defeated the Czech Republic in their opening tie as they move on to the City Finals to face Great Britain.
Her opening 7-6(6), 6-4 triumph over World No 3 Jessica Pegula was a huge confidence boost for the former World No 2, who saved seven set points in the first set to win in two.
Swiatek, who was named Newcomer of the Year in 2020, had an exceptional season in 2022, leading the way in terms of finals appearances, awards won and matches won. She was crowned winner at eight tournaments, including six in a row and a 37-match winning streak.