Rivers connected on 21-of-41 passes for 200 yards, with seven completions going to Danario Alexander for 88 yards and a pair of scores.
The Chargers notched their first-ever regular-season win over Pittsburgh despite the return of Steelers quarterback Ben Roethlisberger, who sat out the previous three games with a sprained right shoulder and a rib injury.
Roethlisberger responded by going 22-of-42 through the air for 285 yards, three scores and an interception for the Steelers (7-6).
Mike Wallace led Pittsburgh's receivers with seven catches for 112 yards and two touchdowns.
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