The Packers (13-1) had not lost in almost a full calendar year, having won 19 in a row since a 31-27 loss at New England on Dec. 19, 2010.
The Chiefs (6-8), who six days ago fired coach Todd Haley, got four field goals from Ryan Succop and a 1-yard scoring run in the fourth quarter from Jackie Battle.
The 1972 Miami Dolphins remain the last National Football League team to go undefeated through an entire season.
While the Packers were losing their first game of the season, the Indianapolis Colts were winning their first by defeating the Tennessee Titans 27-13.
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