Hoping to rebound from their road loss to the Colts, the Broncos went home for a Week 5 divisional duel with the San Diego Chargers.  In the first quarter, Denver trailed early as Chargers QB Philip Rivers got a 2-yard TD run, while LB Brandon Siler returned a fumble 23 yards for a touchdown.  In the second quarter, the Chargers continued its offensive revival with kicker Nate Kaeding getting a 26-yard field goal.  Afterwards, the Broncos would get their only score of the game, as kicker Jason Elam got a 30-yard field goal.  San Diego would end the half with Kaeding nailing a 45-yard field goal. In the third quarter, Denver continued to get pounded with Rivers completing a 9-yard TD pass to TE Antonio Gates and a 15-yard TD pass to WR Vincent Jackson.  In the fourth quarter, San Diego sealed their victory with RB Michael Turner getting a 74-yard TD run for the only score of the period. With their third-straight loss, not only did the Broncos fall to 2-3 entering their bye week, but the loss marked their worse home loss since losing to the Kansas City Chiefs 56-10 on Oct 23, 1966.  The 38-point deficit also marked Denver's worst home loss since the AFL-NFL merger.
Question: In which quarter Denver trailed as Chargers QB Philip Rivers?
Answer: In the first quarter