Perth - World number one Rafael Nadal vowed to raise his game in the ATP Cup knockout stages after overcoming an error-strewn performance against Japan's Yoshihito Nishioka on Wednesday.
The 19-time Grand Slam winner made 36 unforced errors before beating Nishioka 7-6 (7/4), 6-4.
Unbeaten Spain - who won the revamped Davis Cup in Madrid in November - finished top of Group B with world number 10 Roberto Bautista Agut downing Go Soeda 6-2, 6-4 to secure the tie.
Nadal then teamed up with Pablo Carreno Busta to complete the sweep with a 7-6 (7/5), 4-6, 10-6 victory over Go Soeda and Ben McLachlan in the doubles.
Nadal has yet to drop a set in the singles but he looked sluggish at times ahead of the Australian Open, where he could equal Roger Federer's record tally of 20 Grand Slam titles.
The Spaniard, however, believed he was rounding into form.
"I think it's been a positive week for me winning against three tough opponents," he said. "It's going to be tough in Sydney. I really hope to be ready to increase my level."
The long exchanges against an unwavering Nishioka seemed to take a physical toll on Nadal, who appeared weary in Spain's first day-session tie in the hot Perth conditions.
"It was my first experience (this season) with the heat here in Australia, so we played under heavy conditions and it was tough," he said.
Nadal struggled to find his rhythm against the defensive prowess of 24-year-old Nishioka, who counter-attacked superbly to break twice in an engrossing first set, but couldn't close it out in the 10th game.
Nadal capitalised and drew first blood after claiming a tense tie break.
The 33-year-old remained under pressure in the second set and was forced to fend off three break points in the sixth game, before eventually pulling away.
Japan surprisingly finished second in Group B after world number 13 Kei Nishikori and Yasutaka Uchiyama, their third best player, withdrew before the tournament but missed out on a ticket to Sydney.
World number 72 Nishioka has steadily become a fan favourite after earlier beating higher ranked players Nikoloz Basilashvili and Pablo Cuevas.
In the earlier singles, world number 10 Bautista Agut has had a soft start to the season, losing just three games against ATP Tour debutants Franco Roncadelli and Aleksandre Metreveli.
He was made to work harder against world number 119 Soeda, but proved far too strong and broke three times in the 79-minute match.
In the later dead rubber Group B tie, Georgia had a consolation victory over Uruguay when world number 26 Basilashvili beat Cuevas 6-4, 1-6, 6-4.
There was a dramatic moment late in the first set when Cuevas threatened to forfeit after receiving a code violation only to be talked out of it by Basilashvili.
World number 329 Metreveli beat 19-year-old Roncadelli 6-2, 6-1 in the earlier singles.