San Diego Chargers tight end Antonio Gates scored his 100th touchdown Monday night.

Gates, who became the ninth player in NFL history to reach that milestone, scored on a 12-yard pass from Philip Rivers in the first quarter against the Pittsburgh Steelers. Gates sits behind just Tony Gonzalez for touchdowns scored by tight ends.

Gates was added to the Chargers' active roster after serving a four-game suspension for testing positive for a performance enhancing drug. Safety Adrian Phillips has been waived to make room for Gates.

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The Chargers will be without two starters on the offensive line against the Steelers, tackle King Dunlap and guard Orlando Franklin. Receiver Stevie Johnson also is inactive.

The Associated Press contributed to this report