World number one Rafael Nadal steered Spain into the ATP Cup quarter-finals Wednesday despite an uncharacteristically error-ridden performance, with Argentina also powering through.
After six days of round robin play at the inaugural team event across Sydney, Brisbane and Perth, eight teams are left standing from the 24 that started.
Australia, Serbia, Russia and Britain booked their spots in the knockout phase on Tuesday, with Spain – who won the revamped Davis Cup in Madrid in November – and Argentina rounding out the six group winners.
Belgium and Canada joined them as the two best-placed runners-up.
"It was important the first set, and then in the second I had some tough moments but at the same time I was able to manage well to have a break at the right moment, so happy for the victory," said Nadal, who is yet to drop a set.
"I played against a player that started the season on fire winning two great matches against two very good opponents and with very comfortable results.
"So it's a positive victory for me and it's an important victory for the team. We go to Sydney with the confidence that we didn't lose a match yet."
"I really am really happy with the challenges that I've had in the last six, seven days here, and hopefully that can allow me to build my form for Sydney and Melbourne later," said world number two Djokovic.
"Sydney's got a big Serbian community, hopefully the support can be as good as it was here, even better."
In other action, emerging Polish young gun Hubert Hurkacz upset world number four Dominic Thiem for his third win over a top 30 player at the tournament after beating Diego Schwartzman and Borna Coric.
Poland's 2-1 win over Austria ended Thiem's team's chances of topping their group, leaving Croatia and Argentina to battle it out to secure an automatic quarter-final place.
Left-hander Guido Pella got Argentina off to a strong start, defeating former world number three Marin Cilic 7-6 (7/1) 6-3, before a focused Schwartzman crushed Coric 6-2, 6-2.