The 49ers weren't quite sure what they'd get out of Michael Crabtree this season.When Crabtree tore his Achilles' tendon in May workouts, he underwent surgery the next day and promised to return to the team in November.But Achilles' injuries are severe and wide receivers need to be explosive, and there was no telling how effective Crabtree would be.Now four games into his comeback, Crabtree has erased all doubts. In games against the Rams, Seahawks, Bucs and Falcons, he has 16 catches for 255 yards and a touchdown, and in Monday night's victory over the Falcons he played a key role.Though linebacker NaVorro Bowman's interception return and a nothing-but-runs fourth quarter drive for a touchdown justifiably captured the focus of 49ers fans in San Francisco's 34-24 victory, it was Crabtree who helped ignite his team's offense in the second half.After the 49ers trailed 10-3 at the half, San Francisco's offense got going in the third quarter to set the tone for a 31-point explosion.On the 49ers' first third-quarter possession, Crabtree's 47-yard reception took his team to the Atlanta 31-yard line. Two plays later, quarterback Colin Kaepernick found Crabtree again for 19 yards to the...