Hoping to snap a three-game losing streak and give rookie QB Jay Cutler his first NFL win, the Broncos flew to Qualcomm Stadium for an AFC West rematch with the San Diego Chargers. In the first quarter, Denver trailed early as QB Philip Rivers completed a 12-yard TD pass to TE Antonio Gates, while FB Lorenzo Neal got a 4-yard TD run. In the second quarter, the Broncos managed to get on the board with kicker Jason Elam's 34-yard field goal. However, San Diego's dominance continued with RB LaDainian Tomlinson's 1-yard TD run, along with a 7-yard TD pass from Rivers to Gates. In the third quarter, the Broncos showed some signs of life as Cutler completed a 28-yard TD pass and an 11-yard TD pass to rookie TE Tony Scheffler, while Elam nailed a 33-yard field goal. However, in the fourth quarter, the Chargers pulled away with kicker Nate Kaeding's 34-yard and 35-yard field goal, while Tomlinson broke the single-season TD record with a 6-yard and a 7-yard TD run. With their fourth-straight defeat, Denver fell to 7-6.

Based on the above article, answer a question. How many yards was Rivers first TD pass?
12