Rafael Nadal overcame a tough challenge from Yoshihito Nishioka, with his 7-6(4), 6-4 ATP Cup victory which took more than two hours.
The world No. 1 was tested in a 66-minute opening set in Perth, forced to twice recover from a break down before finally accelerating away in the second set to put his country into the last eight.
Spain will travel to Sydney as the new 24-nation event wraps up at the weekend with a week to spare before the January 20 start of the Australian Open.
Nadal was pleased to put Spain through after teammate Roberto Batista Agut beat Go Soeda 6-2, 6-4.
“Today the match was more difficult, it was my first with the sun, with the heat. The ball feels much different, it’s flying more,” the 10th-ranked winner said.
“The ball is flying more. The court is faster. I had more difficulties today, but I handled them well.”
Nadal agreed with his teammate’s assessment.
“This was my first day match playing in these heavy conditions,” Nadal said. “The feeling, the court was different.
“Today was a tough match, Nishioka played very well.”
Nadal, whose won the Davis Cup title with Spain less than two months ago in Madrid, admitted he revels in team competitions.
“I enjoy sharing these experiences with friends, he said of the tight-knit Spanish side.
“I’ve had a lot of success playing for my country. We are looking forward to Sydney (quarter-final on Friday night). We are hoping for more of it.”
Spain joined Serbia, Britain, Russia and Australia in the Sydney quarter-finals as the event wraps up on Sunday.