Only seven minutes later it was 2-0 when Xavi himself latched on to a pinpoint pass from Dani Alves, beating one defender before smashing the ball home.
Cesc Fabregas hit the post and then stabbed home Barca's third on the stroke of halftime as the Spanish champions threatened to run riot in front of a crowd of 68,000.
The former Arsenal midfielder came within a whisker of another goal moments after the restart, forcing a magnificent save from Cabral.
Player of the tournament Messi made it 4-0 eight minutes from time, bursting past Cabral at breath-taking speed to slip the ball into the net and complete the rout.
"It's beautiful to be world champions but it's a team effort," said Messi. "We often play like that but because it was a final it seemed more beautiful."
Asked whether he had adopted a 3-7-0 formation, Guardiola shrugged: "I don't think we were playing 3-7-0. That's just how we play. We try to control the midfield and exploit space.
Barcelona beat Al-Sadd to reach Club World Cup final"We wanted to suffocate the supply to Neymar, who we know is a dangerous player, and to Borges.
"There is no special secret to our success. I am just blessed to work with such terrific players who want to keep on winning. They deserve all the credit."
Santos, who lifted their third Libertadores Cup in June almost 50 years after Pele led them to back-to-back titles in 1962 and 1963, had no answer to Barcelona's brilliance.
"It may have looked easy but it certainly wasn't," said Barca captain Carles Puyol. "The early goals made it easier for us."
Puyol sent a 'get-well' message to Spain striker David Villa, who suffered a sickening leg break in Barca's 4-0 semi-final victory over Qatar's Al Sadd.
"I will give him a (victory) T-shirt," said Puyol. "He really wanted one. He is not here but he is part of the team and this victory.
"We never doubted ourselves and kept their forwards under control. It was a complete performance."
Neymar looked shell-shocked after the game.
"It's impossible to stop Barcelona," said the 19-year-old pin-up, biting his tongue. "But we are the second-best team in the world and for us that is a great reward."