Chelsea, who had been under pressure to win the tournament after becoming the first holders to exit the Champions League at the group stage, missed a string of chances.
"It doesn't matter how skilful the opposition is, our players have the work-rate, energy and teamwork to overcome," Corinthians coach Tite told reporters after the final ended 1-0.
"They have a great telepathy," added the 51-year-old, who guided the Sao Paulo club to the Brazilian title in 2011 and the Libertadores Cup earlier this year.
Their smash-and-grab over Chelsea completed a remarkable turnaround after Corinthians were relegated at the end of 2007.
"With this tournament and the Libertadores Cup we've now gone 16 games and conceded only four goals," said Tite. "The way we managed the game was excellent."
Gary Cahill, sent off in the last minute, Fernando Torres and Victor Moses were denied by brilliant saves from goalkeeper Cassio in a game the English side largely dominated.
Corinthians, who won the first Club World Cup in 2000, caught Chelsea cold when Peru striker Guerrero headed home from close range after Danilo's shot looped up off Cahill's boot.
"I'm delighted to have scored two goals," said Guerrero, scorer of his side's winner in their 1-0 semi-final victory over Egypt's Al-Ahly.
"But it's more important for Corinthians to be world champions.
"We knew that it would be extremely tough to beat the champions of Europe but we gave 100 percent and more. I think we deserved to win the cup."
Torres had a late effort superbly blocked by tournament MVP Cassio and a stoppage-time header ruled out for offside.
The Corinthians players celebrated by dancing and hugging each other as fireworks exploded and some 15,000 travelling fans among the crowd of 68,000 began a fiesta set to go on all night.
Chelsea's interim manager Rafael Benitez refused to make excuses after his second loss in three appearances with three different clubs at the FIFA tournament.
"They had one chance and scored," said the Spaniard. "We didn't take our chances. We had four clear chances and we didn't take them. That was the difference."
Cahill's red card, for kicking striker Emerson in retaliation for an elbow in the face, had no bearing on the result, said Benitez.
"He lost his temper but it didn't make a difference to the result," said Benitez, who will be without Cahill for Chelsea's League Cup quarter-final at Leeds United on Wednesday.
Cahill expressed regret but blamed Emerson's theatrical tumble for convincing the referee to send him off.
"I've tackled the guy, we tangled legs and he lashed out with his arm and hit me in the face," said Cahill. "I'm angry about it, but also at my reaction.
"I touched him in the shin - it probably wouldn't have knocked over my one-year-old daughter yet he's rolling around five or six times."
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