Knowshon Moreno scored on a 3-yard run with 8:15 left in the fourth quarter for a 24-7 Denver advantage, but the Broncos had to withstand a late rally from the Chargers to secure the win and land a spot against New England in next week's AFC title match.
Philip Rivers connected with Keenan Allen on a 16-yard scoring strike with 5:49 left, cutting San Diego's deficit to 10 points.
The Chargers then recovered the ensuing onside kick and Nick Novak followed with a 30-yard field goal to make it a one-score game, but San Diego could get no closer.
Moreno finished with 82 rushing yards on 23 carries.
Rivers went 18-of-27 through the air for 217 yards and two scores, both to Allen, who ended with six grabs for 142 yards.