Coming off their thrilling overtime divisional road win over the Seahawks, the 49ers went home for a Week 3 duel with the Detroit Lions.  In the first quarter, the Niners struck first as QB J.T. O'Sullivan completed a 6-yard TD pass to WR Isaac Bruce.  In the second quarter, San Francisco increased its lead with RB Frank Gore getting a 4-yard TD run.  Striking again, Delanie Walker caught a touchdown pass shortly before half-time.  The Lions would respond with kicker Jason Hanson getting a 44-yard, yet the 49ers replied in the fourth quarter with CB Allen Rossum getting a 1-yard TD run.  Detroit tried to rally as QB Jon Kitna completed a 34-yard TD pass to RB Rudi Johnson, yet San Francisco sealed their victory with kicker Joe Nedney nailing a 25-yard field goal.. Which team led at halftime?