Australia has lost its opening United Cup tie against Great Britain after Alex de Minaur and Ajla Tomljanović were defeated in their respective singles rubbers in Perth on Friday night.

De Minaur, ranked 12th on the ATP Tour rankings, looked rusty against Cameron Norrie, losing 6-4, 2-6, 7-6 (7/2) in two hours and 20 minutes.

Great Britain then raced out to an unassailable lead in the tie after world number 56 Katie Boulter defeated Tomljanović 6-2, 6-4.

Storm Hunter and Matt Ebden earned a 6-3, 7-6 (7/5) win over Boulter and Neal Skupski in the mixed doubles rubber to ensure Australia reduced the final deficit to 2-1.

Australia's quest to reach the quarterfinals will rely on reigning champions USA beating Great Britain on Sunday, before it needs to defeat the Americans the following day.

"It's the start of the year. You don't want to base your whole year on one match," de Minaur said.

"Sometimes there's a little bit of rust. The last couple of years I probably haven't started my best.

"Ultimately, my focus is the Australian Open.

"Obviously I want to play well for my country and I'll do my best to bounce back and be raring for the next one."

Earlier in the day, Spain clinched its tie against Brazil 2-1.

AAP/ABC