Coming off their home win over the Dolphins, the Chargers flew to Heinz Field for a Week 4 Sunday night duel with the defending Super Bowl champion Pittsburgh Steelers.  San Diego found themselves in a huge deficit in the first half.  In the first quarter, the Steelers opened the game with running back Rashard Mendenhall getting a 1-yard touchdown run and quarterback Ben Roethlisberger completing a 19-yard touchdown pass to running back Mewelde Moore.  Pittsburgh would increase their lead in the second quarter with Mendenhall's 2-yard touchdown run. In the third quarter, the Steelers continued to roll as Roethlisberger found tight end Heath Miller on a 6-yard touchdown pass.  San Diego would strike back as quarterback Philip Rivers threw a 3-yard touchdown pass to tight end Antonio Gates.  In the fourth quarter, the Chargers began to catch up with a key play on special teams as fullback Jacob Hester stripped Stefan Logan of the ball and returned it 41 yards for a touchdown.  Pittsburgh would answer with Roethlisberger's 6-yard touchdown pass to Miller.  Afterwards, San Diego continued its comeback run as Rivers completed a 30-yard touchdown pass to Gates and a 13-yard touchdown pass to wide receiver Chris Chambers.  However, the Steelers came right back with a 46-yard field goal from kicker Jeff Reed.  The 'Bolts tried to cap off their rally, but a sack and fumble by linebacker James Harrison led to a Pittsburgh recovery, effectively ending any hope of a comeback.. How many touchdowns were scored in the first half?