DETROIT -- David Akers nailed a 55-yard field goal on the final play of the first half to give the 49ers a 12-10 lead over the Detroit Lions at halftime.The 49ers led despite getting called for 11 penalties for 99 yards.Frank Gore had five rushes for 66 yards, including a 47-yard gallop late in the first quarter to lead to the 49ers' only touchdown. Gore punched it across from a yard out, following the block of right tackle Anthony Davis against Lions defensive tackle Ndamukong Suh.The 49ers managed to keep Lions receiver Calvin Johnson in check through two quarters. Johnson had three catches for 29 yards, as Tarell Brown and rookie Chris Culliver did a good job of limiting the big play.Alex Smith completed 11 of 15 attempts for 77 yards in the first half. Michael Crabtree led the 49ers with five catches for 32 yards. Ted Ginn, who drew the starting assignment, had two receptions for 24 yards, as the 49ers drove late in the first half for the go-ahead score.Rookie Aldon Smith had a sack of Lions quarterback Matthew Stafford in the end zone for a safety to pull the 49ers within 10-9 in the middle of the second quarter. (The sack was initially credited to Ray McDonald.)Things got off to a rough start for the 49ers, as they fell behind 10-0.On the first snap of the game, 49ers left tackle Joe Staley had barely gotten out of his stance when defensive end Kyle Vanden Bosch exploded around him to sack and strip the ball from quarterback Alex Smith.That play led to a Jason Hanson field goal, and a 3-0 Lions lead.Before the 49ers could run another offensive play, tight end Vernon Davis and Anthony Davis were called for false starts.The Lions added a touchdown on Stafford's 16-yard pass to tight end Brandon Pettigrew.