Holders Serbia avoided any more scares to complete a 4-1 victory over India in the Davis Cup on Sunday and Germany joined them in the quarter-finals as Philipp Petzschner edged them to victory in a thriller in Croatia.
The United States also booked a home quarter-final against favourites Spain as Andy Roddick gave them a 3-1 lead in Chile with victory over Paul Capdeville.
Spain, Argentina and Sweden had all wrapped up their World Group first round ties by taking unassailable leads over Belgium, Romania and Russia respectively on Saturday.
World number one Rafael Nadal used Sunday's "dead rubber" as some useful practice, beating Belgium's Olivier Rochus 6-4, 6-2.
Unfancied India had fought toe-to-toe with Serbia in Novi Sad during Friday and Saturday to trail 2-1 but Serbia's Viktor Troicki, playing as his country's top player in the absence of world number three Novak Djokovic, finished the job.
Troicki, who won the decisive fifth rubber when Serbia beat France in last year's final in Belgrade, was too strong for Somdev Devvarman, winning 6-4, 6-2, 7-5 in the first reverse singles to set up a July quarter-final in Sweden.
"It is a great feeling to be in the last eight of the competition because this means we have stayed in the World Group, while it also gives us a chance to carry on with our title defence," Troicki told reporters.
"We are through to the quarter-finals, we know it's going to be very tough against Sweden and we hope to have our best player Novak Djokovic back for that tie."
Australian Open champion Djokovic skipped the tie to concentrate on the Indian Wells event which begins this week.
In Zagreb, 2005 champions Croatia levelled at 2-2 with Germany after Marin Cilic defeated Philipp Kohlschreiber 6-2, 6-3, 7-6 but Ivo Karlovic, who in Saturday's doubles broke Andy Roddick's serving speed record with a 156mph rocket, was beaten by Petzschner 6-4, 7-6, 7-6.
"I got so much support from my team mates," Petzschner told reporters. "It is just unbelievable that it ends like this. Absolutely crazy."
In the remaining ties, France and Austria were locked at 2-2 in Vienna while the Czech Republic were in danger of a shock exit against World Group debutants Kazakhstan after Andrey Golubev beat Tomas Berdych to level the match at 2-2.