Kansas City held the Angels to two hits through seven innings, but wildness on the part of the relief corps led to the Los Angeles comeback.
Jamey Wright and Roman Colon combined to walk the bases loaded in the eighth before Guerrero singled to left. Kansas City pitchers walked eight batters overall.
Brian Fuentes gave up a lead-off single in the bottom of the ninth, then got Yuniesky Betancourt to ground into a double play en route to his 38 save.
Jered Weaver (14-5) gave up nine hits over seven innings, but still picked up the victory. Wright (1-5), the third of five Los Angeles pitchers, took the loss.
Los Angeles remained 3 1/2 games in front of Texas for the lead in the American League West.