Take a look at the play diagram:
NMSU ran a man-to-man defense on third and short, and they decided to send 6 defenders to the quarterback (4 defensive linemen and 2 blitzing linebackers from each end). The red lines on the diagram indicate which defenders were responsible for their respective offensive receiver. The key to this play was the blocking by the UGA offense, particularly Brandon Harton. The Georgia offensive line blocked to the right, and Harton -- who lined up to the right of Murray -- had to come all the way across to block the blitzing backer on the opposite side. Yes, on the replay you will notice he got knocked straight back, but he did enough to keep his guy from getting to Murray.
As for the receivers, any type of horizontal route makes things very difficult for a man-to-man defense, especially when offensive players start crossing in front of each other. On this play, the two outside receivers on the left side, Conley and Bennett, both run quick "square in" routes, while Aron White -- the inner-most receiver on the same side -- runs a short "corner route" to the back pylon. The break to the corner was too much for the defender to handle, and White ends up getting a couple of steps ahead. The result is a pretty easy TD catch...and White getting in touch with his "green" side: