Answer based on context:

Coming off their road win over the Raiders, the Chargers would play their Week 2 home opener against the Baltimore Ravens.  San Diego would deliver the opening strike in the first quarter as quarterback Philip Rivers completed an 81-yard touchdown pass to running back Darren Sproles.  The Ravens would respond with running back Willis McGahee getting a 5-yard touchdown run, yet the Chargers would regain the lead as kicker Nate Kaeding got a 29-yard field goal.  Baltimore would take the lead in the second quarter as McGahee got a 3-yard touchdown run.  San Diego would pull within one as Kaeding made a 22-yard field goal, but the Ravens answered with quarterback Joe Flacco completing a 27-yard touchdown pass to wide receiver Kelley Washington.  The Chargers would end the half as Kaeding would make a 23-yard field goal. In the third quarter, Baltimore would add onto their lead as Flacco completed a 9-yard touchdown pass to tight end Todd Heap.  San Diego would stay close as Rivers completed a 35-yard touchdown pass to wide receiver Vincent Jackson.  In the fourth quarter, the Chargers got closer as Kaeding kicked a 25-yard field goal, but the Ravens would answer with kicker Steve Hauschka nailing a 33-yard field goal.  San Diego would manage to get a late drive all the way to the Ravens' 15-yard line, but on 4th-&-2, Sproles was tackled behind the line of scrimmage by an unblocked Ray Lewis, ending any hope of a comeback.

How many yards was the longest touchdown?
81