Scotland, Australia and the Netherlands crashed out of the Betfair World Cup of Darts in the second round, while defending champions England were extended to a deciding leg by South Africa.
Antonio Alcinas and Carlos Rodriguez won the final two legs as Spain shocked Scotland's Gary Anderson and Robert Thornton by a 5-4 scoreline at the Alsterdorfer Sporthalle in Hamburg.
"It's great for us," said Rodriguez. "We'll look forward to tomorrow and anything can happen now. It's very important for us both when we're playing for Spain, we are very proud and every time we get results like this it gets more people in Spain playing darts."
Spain will take on Wales in quarter-finals after Mark Webster and Richie Burnett beat Canada's John Part and Jeff Smith 5-2.
Australians Simon Whitlock and Paul Nicholson, last year's beaten finalists, were thrashed 5-1 by Belgium's Huybrecht brothers, Kim and Ronny, who finished with a 101.08 average and will take on Croatia in the last eight.
Robert Marijanovic and Tonci Restovic beat Northern Ireland's Brendan Dolan and Michael Mansell 5-4 in the opening match on Saturday evening.
South Africa's Charl Pietersen missed two match darts in the deciding leg to send England packing before Adrian Lewis, partnering world champion Phil Taylor, stepped up to take out a 58 checkout to seal a 5-4 victory.
England will play Japan next after Haruki Muramatsu and Sho Katsumi saw off Republic of Ireland duo William O'Connor and Connie Finnan 5-3.
Raymond van Barneveld and Michael van Gerwen were another seeded duo to fall in the last 16, Jani Haavisto and Jarkko Komula coming from 2-0 down to earn Finland a 5-3 success over the Netherlands.
Haavisto and Komula's reward is a quarter-final against Germany. Jyhan Artut and Andree Welge saw the host nation through with a 5-2 win over Poland's Krzysztof Kciuk and Krzysztof Ratajski in the final action of the night.
Will Phil 'The Power' Taylor be the man to beat in 2013?