Guerrero pounced decisively on 69 minutes to deny Rafa Benitez his first trophy as Chelsea boss as the European champions finished with 10 men after Gary Cahill was sent off late on.
Goalline technology has been available in the competition and it almost came into use on 10 minutes when Cahill's prodded shot was stopped on the line by Corinthians goalkeeper Cassio.
The first half lacked any real tempo as Corinthians did well to stifle Chelsea, although the Brazilians did carry a threat, with Emerson wastefully blazing over on 29 minutes after Cahill had failed to cut out Guerrero's pass.
Guerrero wriggled free from the Chelsea defence on 35 minutes, but scuffed his shot off target and Emerson fired the loose ball against the base of the post from an acute angle.
Chelsea perked up in the final 10 minutes of the opening period and Fernando Torres showed excellent control to bring down Frank Lampard's long ball before hitting a tame volley at Cassio.
The Corinthians keeper then produced the save of the half, diving full length to tip Victor Moses' curler around the post before making a more routine stop from Juan Mata's dipping drive.
The second half started much livelier and Cassio was again called into action on 54 minutes as he rushed out to thwart Eden Hazard following a fine through ball from Mata.
Paulinho flashed a shot wide before Corinthians made the breakthrough on 69 minutes as the unmarked Guerrero headed home from close range after Danilo's shot had looped into the air off Cahill.
Benitez threw on Oscar in search of an equaliser and the golden chance arrived four minutes from time when the ball broke to the unmarked Torres six yards out, but the Spanish striker could only drill his shot at Cassio's legs.
Cahill was shown a red card in the last minute after an off-the-ball incident involving Emerson before Torres was rightly denied the equaliser by the offside flag after he had glanced home Oscar's ball into the box.