'I'm not going to lie': Ajla Tomljanovic's admission after another loss at the United Cup

Ajla Tomljanovic was reasonably happy with her performance against the USA's Jessica Pegula despite losing in straight sets on Monday night.

Tomljanovic, 30, was broken early in their United Cup match in Perth, before breaking back and forcing a tiebreak, which she lost 8-6.

World No.5 Pegula then won the second set 6-3.

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While she lost, the Aussie - who has slipped to No.292 in the world following a string of injuries - felt better than she did during a 6-2, 6-4 loss to Great Britain's Katie Boulter on Friday.

"I'm not going to lie, Friday really kind of put me down," Tomljanovic said on Monday night.

"I really thought my level wasn't there.

"But coming out today and putting up a good fight, and even though I didn't win, I felt like I had so many chances."

Australia qualified for the quarter-finals of the United Cup by downing USA on Monday night.

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Alex de Minaur blitzed world No.10 Taylor Fritz 6-4, 6-2, before countrywoman Tomljanovic fell to Pegula.

The doubles pair of Matt Ebden and Storm Hunter then had to win in straight sets for the Aussies to top their group.

They did so, beating USA 6-3, 6-1 to clinch victory and a quarter-final spot.

"They played fantastic, it was great," team captain Lleyton Hewitt said.

"I'm very proud. It was backs against the wall after our first match.

"They left everything out there. It bodes well for Wednesday night."

The victory sets up a potential clash with Serbia in the quarters, potentially pitting de Minaur against Novak Djokovic.