Australia hasn't exactly set the world on fire at the United Cup but teammates Jason Kubler and Maddison Inglis have given fans something to cheer about with news that they're the latest stars from down under to find romance on the tour.

Inglis was seen cheering on her partner as he came from behind to beat Dan Evans in straight sets during the Aussies' 3-2 loss to Great Britain last Friday, and she's bound to do the same when he tackles the Open from January 16.

The pair are remaining tight-lipped about their relationship, refusing to post photos of each other on their social media accounts - but rumours the pair are romantically linked have been going for months.

While Kubler's sensational 6-3 7-6 (7-3) defeat of the highly fancied world No.27 was easily the highlight of the Aussies' opening tie of the United Cup, Inglis had a far harder time of it.

She, Alex de Minaur and Zoe Hives were all outplayed after a disruptive lead-in to the tournament at Sydney's Ken Rosewall Arena.

De Minaur was promoted to Thursday's top-seeded men's match-up after Nick Kyrgios pulled out with an ankle injury and Inglis was rushed in only hours before Friday's match when Ajla Tomljanovic went down with a knee complaint.

Replacing the world No.33 was a tough ask for No.180 Inglis, who had not been expecting to play in the tournament at all and was bed-ridden with a stomach bug as recently as last Wednesday.

Inglis needed to defeat world No.98 Harriet Dart on Friday evening to give Australia any hope of salvaging the tie but dropped the first set after errors began creeping into her game and eventually fell 6-4 6-4.

She will be battling through the qualifiers to get a spot in the Australian Open, whereas Kubler will be looking to improve on the first-round exits he suffered in the men's singles in 2018 and 2019.

He had a great 2022 campaign, winning through to the round of 16 at Wimbledon and recording his best victory to date when he beat world No.9 Felix Auger-Aliassime in the Hall of Fame Tennis Championships in July.

Kubler's rise comes despite a shocking injury battle earlier in his career that saw him have six operations on his injured knee by the time he was just 24.

At one stage he was down to his last $75 despite being a junior world No.1, and could only play on clay courts from 2012 to 2015 so he wouldn't hurt his knee further.