Top-seeded United States booked an intriguing quarterfinal clash with China at the United Cup after Coco Gauff and Taylor Fritz claimed impressive singles victories on Tuesday.

Italy also made it through to the final eight of the mixed teams tennis tournament after sweeping France in Sydney.

The United States only needed to win one rubber in straight sets against Croatia to top Group A, and world No. 4 Fritz delivered with a comprehensive 6-3, 6-2 victory over Borna Coric in hot conditions at Perth's RAC Arena.

Even though he is ranked world No. 86, ahead of Coric, Fritz was wary, having lost all four previous matches against the 28-year-old Croatian. He stepped up a gear against Coric and played with trademark firepower to clinch a one-sided victory in one hour and 31 minutes.

"I feel like I'm a completely different player from when we have played in the past," said Fritz, a finalist at this year's US Open. "It's great to get that win, especially after the other day [against Felix Auger-Aliassime]."

World No. 3 Gauff locked up victory for the Americans with an easy 6-4, 6-2 win over Donna Vekic. She completely dominated the world No. 19 with trademark power from the baseline and strong serving in her second consecutive outstanding performance.

The former US Open champion has carried on where she left off in her season-ending triumph at the WTA Finals, having earlier in the tournament beaten Canada's Leylah Fernandez.

It was revenge for Gauff after she had lost in straight sets to Vekic in a tempestuous third-round clash at the Paris Olympics.

"Really happy with how I played. The Olympics loss hurt, and it was motivation to do better," Gauff said.

Earlier in Sydney, Italy needed to win just one match against France, and Flavio Cobolli produced a gritty 3-6, 7-6 (8), 6-2 upset win over Ugo Humbert.

It eased the pressure on fourth-ranked Jasmine Paolini, and she secured Italy's victory with a 6-0, 6-2 romp of Chloe Paquet in one hour.

It continued an impressive start to the season for Paolini, a finalist at this year's French Open and Wimbledon, after she had beaten Belinda Bencic on Sunday.

Sara Errani and Andrea Vavassori capped Italy's perfect day with a straight-set victory over Elixane Lechemia and Edouard Roger-Vasselin in the mixed doubles.

The quarterfinals start in Perth on Wednesday, with defending champions Germany playing Kazakhstan in a match-up of group winners, before China and the United States do battle in the night session.

The group stage wraps up in Sydney with host nation Australia tackling Britain, while world No. 2 Iga Swiatek leads Poland against the Czech Republic.