Serbian superstar Novak Djokovic said that the ATP Cup was the ideal preparation for his bid to win an eighth Australian Open crown.
Speaking after Serbia beat Chile 2-1 to remain unbeaten after the round-robin stage, Djokovic said he wasn't fazed by having to play three top players in a row to start the season.
Djokovic made it three wins from three with a 6-3, 6-3 win over Cristian Garin, the world No 33, to win the tie for Serbia after Dusan Lajovic earlier beat Nicolas Jarry 6-2, 7-6.
Jarry and Alejandro Tabilo salvaged some pride for Chile when they beat Viktor Troicki and Nikola Cacic in the doubles 6-3, 7-6.
"I've never minded, to be honest, to face tough adversity from the blocks and have high-intensity matches from day one of the season," Djokovic, a 16-time Grand Slam winner, said.
"I had Kevin Anderson who was playing some extraordinary tennis. I thought it was the toughest match I've played here in Brisbane.
"And again against [Gael] Monfils, even though it was straight sets, it was still a lot of rallies and it was quite long and exhausting.
"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."
Serbia now travel to Sydney, where they will take on the eighth-ranked team in the quarter-finals and Djokovic said he expected to have even more support from Serbian fans there than in Brisbane.
"I'm enjoying it – I enjoy the fact that we will actually go to a different city together, travel today, practice there tomorrow, play in a different environment," he said.
"Sydney's got a big Serbian community, hopefully the support can be as good as it was here, even better.
"It's a team competition, it's how I personally treat it, and that's how it feels for all of us, so having that journey through various places in Australia together feels like a World Cup to us a little bit."
World No 1 Rafael Nadal overcame an error-strewn performance and Yoshihito Nishioka's brave challenge to lead Spain into the quarter-finals.
The 19-time grand slam winner made 36 unforced errors before beating Japan's Nishioka 7-6, 6-4.
Unbeaten Spain – who won the revamped Davis Cup in Madrid in November – finished top of Group B with Roberto Bautista Agut beating Go Soeda 6-2, 6-4 to secure the tie.
"It's the first time I played under these heavy conditions, so the feeling on court is completely different," Nadal, who has yet to drop a set in Australia, said. "I played against an opponent who has started the season on fire."
Japan finished second in Group B and are still in the mix to advance to the knockout stages in Sydney.
World No 4 Dominic Thiem was beaten by Polish youngster Hubert Hurkacz on Wednesday, a result that ends any Austrian hopes of advancing to the quarter-finals, with Poland also out of contention.
Hurkacz went into the match on the back of wins against world No 13 Diego Schwartzman and the 28th-ranked Borna Coric.
Add the 22-year-old claimed another big scalp when he defeated Thiem 3-6, 6-4, 7-6 in Sydney. "Dominic is a great player, the way he played the first set was unbelievable. He brought out the best in me," Hurkacz said.
