Context: Riding high from their win over Pittsburgh, the Chargers traveled up north to Candlestick Park for a Week 6 fight with their other state rival, the San Francisco 49ers.  In the first quarter, San Diego struck first as QB Philip Rivers completed a 57-yard TD pass to TE Antonio Gates, yet the Niners tied the game with QB Alex Smith completing a 15-yard TD pass to WR Bryan Gilmore. RB LaDainian Tomlinson helped the Chargers retake the lead, as he got a 5-yard TD run.  In a topsy-turvy second quarter, points were flying everywhere.  It began with 49ers kicker Joe Nedney kicking a 42-yard field goal.  Afterwards, the Chargers retook the lead as Rivers hooked up with WR Vincent Jackson on a 33-yard TD strike, followed by Tomlinson getting a 1-yard TD run.  Then, Smith connected with FB Moran Norris on a 2-yard pass for San Francisco, which was followed up with the Niners getting a safety from an intentional grounding penalty. Tomlinson would get another 1-yard TD run to end the quarter.  In the second half, San Diego scored 13 unanswered points to seal the game, with kicker Nate Kaeding kicking two field goals (24-yarder in the third quarter and a 44-yarder in the fourth quarter) and Tomlinson iced the game with one more 5-yard touchdown run.  With their victory, the Chargers improved to 4-1

Question: Who scored the first touchdown?

Answer:
TE Antonio Gates