Inaugural champions the United States and Italy handed out identical 3-0 thrashings to Croatia and France respectively, to top their groups and sail into the quarter-finals of the United Cup on Tuesday.
Taylor Fritz's 6-3, 6-2 win against Borna Coric in men's singles ensured the U.S., who meet China in the quarter-finals, topped Group A regardless of the outcome of the tie in the mixed team tournament.
The big-hitting American converted his only break point of the first set in the seventh game and then served out the opener to surge ahead.
He capitalised on a double break to go 4-0 up and went on to secure his maiden win against Coric in 91 minutes.
Coco Gauff was equally dominant in her 6-4 6-2 win over Donna Vekic in women's singles.
Vekic upset Gauff at the Paris Olympics and went on to win the silver medal, but in Perth the American dictated terms as she secured the tie for her team even before the mixed doubles rubber.
After racing to a 4-1 lead in the first set, former U.S. Open champion Gauff never really took her foot off the pedal.
"I'm really happy with how I played today," Gauff said.
"She's a great player, and the Olympics loss hurt, so I definitely was thinking about it today as motivation to do better."
Gauff and Fritz were equally impressive in their mixed doubles win.
Earlier, Italy's Flavio Cobolli saved a match point to get the better of Frenchman Ugo Humbert 3-6 7-6(8) 6-2 in Group D in Sydney.
Humbert won his first 17 service points in the second set and was serving for the match at 6-3 5-4 before Cobolli produced a stunning comeback.
"It was a great battle to start the season. I'm really happy about the match," Cobolli said.
"I think I played a really good match and also it was tough to come back (against) Ugo." Italy clinched the tie with a match to spare when Jasmine Paolini swept aside Chloe Paquet 6-0 6-2 in women's singles.
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