1. The first touchdown of the game.
The 49ers are lined up with 2 wide right and a third man going in motion towards the right. The Bears are running man coverage. The free safety (Chris Conte) takes the man in motion.
With the front four, the Bears are able to collapse the pocket and bring pressure to Colin Kaepernick. Two Bears defenders nearly get to the quarterback.
3. Brandon Marshall touchdown.
In a stark contrast to the routes Trestman had Marshall and Jeffery running earlier in the game, the Bears coaching staff realized that with bum ankle and hamstring, respectively, quick cuts and sharp turns wouldn't beat the 49er corners.
Tim Jennings is a probowler. Charles Tillman is arguably the greatest cornerback in Chicago Bears history. However, Kyle Fuller brings attitude, confidence, and a speed the other two don't have. As his man starts to run his route, you can see Fuller turning his hips from the backpedal ready to either run with the receiver or turning back and driving toward him.
Earlier in the game, the corners of the 49ers realized Marshall and Alshon were not going to challenge them deep due to nagging injuries. Here you have Marshall running a curl route. Typically this is effective when the corner is playing off and you can make a sharp turn.
Based on the Bears defensive look, they should be prepared to stuff a run. You have 7 in the box with the 8th looking to cheat down into the box.
Where the play goes bust is that Jared Allen overruns the play, losing his contain and position. Then Bostic cheats to the middle of the field. Since the 49ers formation was heavy to the top of the screen and the safety already cheated in, it left a gaping hole and nobody had the angle or position to stop the run. Touchdown 49ers.