Home favourite De Minaur delighted the Sydney crowd by recovering from a set and break down to claim his maiden win over the world No.2.

"I think it's definitely up there [as one of my best wins]," he said. "It's one of those achievements that you have unlocked in your career.

"But also, it's a big win for myself, one that I really needed. I'm going to cherish and use, take all the confidence from this and be able to hopefully take it to have a good [Australian] summer."

Nadal, a 22-time grand slam champion, was also beaten by Great Britain's Cameron Norrie in his opening match at the inaugural team tournament, and is still seeking his first victory of the season with his Australian Open defence just around the corner.

Spain and Australia are unable to progress to the City Finals, but Nuria Parrizas Diaz levelled the Group D tie with a 6-1 6-3 victory over Maddison Inglis.

United States, which required just two points against Germany to advance to the next stage, set up a showdown with Great Britain after Taylor Fritz and Madison Keys enjoyed straight-set successes over Alexander Zverev and Jule Niemeier respectively. 

Italy moved to the brink of the City Finals after taking a 2-0 lead over Norway. Lorenzo Musetti overcame Viktor Durasovic in straight sets, while Martina Trevisan edged out Malene Helgo in three.

Greece requires one win from its final three matches against Belgium to also advance, Stefanos Tsitsipas hit 12 aces on the way to defeating David Goffin 6-3 6-2 to level the Group A showdown at 1-1.

Poland's winner-takes-all Group B clash with Switzerland is also finely poised at 1-1. World No.1 Iga Swiatek beat Belinda Bencic 6-3 7-6 (7-3), before Marc-Andrea Huesler's 6-3 6-2 victory against Daniel Michalski.