Bautista Agut returned after withdrawing on Thursday following the death of his father and the world number nine sealed an emotional 7-6 (7/3), 6-3 victory in Madrid as Spain edged closer to their sixth success in this competition.
Nadal had not lost a Davis Cup singles match since 2004 and it was always going to be a tough task for Shapovalov to send the tie to a deciding doubles rubber.
This is Canada's first ever Davis Cup final in comparison to Spain, who are playing their 10th, albeit first since 2012, when they were beaten by the Czech Republic.
But the young Canadian showed grit and got himself back into the match to force a second-set tie-break and even saved two match points with blistering back-to-back winners, managing to score a set point of his own, but the 20-year-old finally bowed out when he netted a forehand.
"I don't think any of us expected that we could get this far", Shapovalov said.
"It's true that I held up, but we know that playing so many matches in this (hard court) surface is risky for me, something can happen at any time", Nadal said.
The British team complained that Spain made a late change for the first singles match, citing an injury to replace Pablo Carreño Busta by López.
Almost 8% annual GHG cuts required to hit Paris' 1.5C goal
Expressing its concern, United Nations said that drastic action is the only way to avoid the worst effects of climate change . To stop so they agreed on the must decrease emissions and work towards a low-carbon world within decades.
It was however Roberto Bautista Agut's presence, and victory, that was awe-inspiring.
Five of the seven ties in the knockout rounds of the Davis Cup Finals were decided in the doubles matches. "And, well, it was an incredible feeling on the court".
"When you finally win the title after all the things that we went through this week, and playing at home, it is something hard to describe", he said, via the Davis Cup website.
"I had the opportunity to play today because all the team and all the players. did an unbelievable effort since the first day", he said.
Tournament organizer and Barcelona soccer star Gerard Piqué, his wife Shakira - who performed in the closing ceremony - and Spanish King Felipe VI were among those celebrating Spain's triumph. "I came to support the team with all my heart, but once we qualified for the final, I started to feel like playing". It had never beaten the USA or Australia in the Davis Cup.
All four semifinalists are secured in next year's edition of the Davis Cup Finals, which is the result of a 25-year partnership between the International Tennis Federation and the investment group Kosmos to make the team competition more attractive and lucrative.