With top-ranked Spain missing big guns Rafa Nadal, David Ferrer and Nicolas Almagro, the Canadians seized their chance when Milos Raonic and Frank Dancevic dominated the clay-loving Iberians on the lightning fast Vancouver hardcourts.
Raonic, the world number 15, delivered as expected to tame feisty Alberto Ramos 6-7 6-4 6-4 6-4 before Frank Dancevic, ranked 161, destroyed world number 34 Marcel Granollers 6-1 6-2 6-2.
Spain looked determined to make it a difficult day for Canada when Ramos, making his Davis Cup debut, fought off three break points on his opening serve then forced the first set tie-break, which he won 7-5 when rattled Raonic sent his forehand long.
There would be few other miscues, though, as Raonic broke Ramos to open the second set and then collected the decisive break at 4-4 in third on his way to a 2-1 lead.
At 4-4 in the fourth, Raonic broke Ramos again before serving out the match with two thundering aces.
"It wasn't always the prettiest but thankfully I'm through," Raonic told courtside television as the celebration erupted around him. "I just put everything aside and focused on winning.
"I was hoping to turn the match in the first set, I had three early chances on his serve, three forehands into the net, I couldn't change it around there.
"But as soon as I got that first break right away in the second it let me play a little more freely."
Dancevic, still chasing his first career ATP Tour title, dropped to his knees and clenched his fists to celebrate the biggest win of his career when a Granollers return hit the net.
"I think I played the match of my life today," said the 28-year-old.
"I just went in with a lot confidence, like just had to go all or nothing today. Anytime I had an opportunity I went for it.
"This isn't over yet. We've to go strong, these guys aren't finished yet, they're going to come strong tomorrow.
"They've got a great doubles team ... we just have to go hard until the last ball this weekend."
Granollers will team up with Marc Lopez to take on Canada's Daniel Nestor and Vasek Pospisil in a must win doubles match on Saturday if they are to keep alive their hopes of advancing to the quarter-finals.
Spain have not crashed out in the first round since 2006, when they fell 4-1 to Belarus.
John Isner and Sam Querrey used their big serves to blast the United States into a commanding 2-0 lead over Brazil in their first round tie.
Isner sat out the Australian Open with a knee injury but the world number 16 reported fit for duty and recorded a routine 6-3 7-6 6-3 victory over Thiago Alves after Querrey began the day by brushing past Brazilian number one Thomaz Bellucci 6-3 6-4 6-4.
Using his booming serve to full advantage on the lightning quick Jacksonville hardcourts, Isner pounded 32 aces past his overwhelmed Brazilian opponent to leave the US one win away from advancing to the last eight.
The United States, who have won the competition a record 32 times, were back on home turf in Florida after playing all their ties away last year.
The 20th ranked Querrey provided the early fireworks and, firing down 15 aces at Brazilian lefty Bellucci, was in full control throughout his match.
"I thought I served great today the whole day," Querrey, who never faced a break point, said. "This is my first home tie. These Davis Cup weeks are so much fun."
The spotlight now shifts to Saturday for a showdown between Australian Open champions Bob and Mike Bryan and Brazil's Marcelo Melo and Bruno Soares.
The top-ranked Americans, however, can expect a tough test from the Brazilians who hold a 2-1 edge in head-to-head meetings.
Germany's number one Philipp Kohlschreiber pulled out when 5-4 ahead in the fifth set of a gruelling first rubber to hand Argentina the lead in their first round tie.
The world number 19 led 6-3 5-7 6-2 4-6 5-4 against Carlos Berlocq, a stand-in for the absent Juan Martin del Potro, when he pulled his left hamstring after a four-hour marathon played in more than 35 degrees heat.
World number 12 Juan Monaco then beat Florian Mayer 6-7 6-3 6-3 6-4 to put Argentina 2-0 up on the first day on the claycourt at Parque Roca.
"I can't move my leg. I can't take a single step," Kohlschreiber told German reporters in the privacy of the locker room as he waited for a pair of crutches to be able to leave the stadium on the outskirts of Buenos Aires.
"It was a bitter thing for me and the whole team," added the 29-year-old. "It's hard to assess the gravity of the injury until further studies are conducted."
Team captain Carsten Arriens will now have to make a tough decision about who to play alongside Christopher Kas in Saturday's doubles.
Kas was to have teamed up with Kohlschreiber against David Nalbandian and Horacio Zeballos. Arriens now has to choose between Mayer and Davis Cup newcomer Tobias Kamke.
"It's no secret Philipp's already leaving for Germany on crutches ... it's a very difficult situation for us," Mayer told a news conference.
Argentina, normally favourites at home, had started the tie as underdogs given Del Potro's decision not to play the Davis Cup this year to concentrate on the tour and a six-month injury layoff that has left Nabandian short of match practice.
"I can't believe I'm experiencing this," an elated Berlocq, ranked 70, said in a courtside interview.
"The whole team had drummed into me that I could win and at times I looked at the clock and thought 'I'm doing well because I'm tiring him and he has to play all three days'.
"Thank God, I got another chance after the defeat against (Tomas) Berdych," added Berlocq, whose loss to Berdych gave Czech Republic their semi-final victory at Parque Roca last September.
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- Milos Raonic
- Frank Dancevic