Harris's TD run. Milano attempted to fill the gap. He was late AND missed the tackle. Big fail.
What happens after that, as Harris has a head of steam heading into the EZ, is not really the secondary's fault.
Edit: I must be thinking of the long 3rd down run. The Harris TD run, the DT got blown up, Edmunds and the other LB couldn't get off their blocks and Marlowe had to make a diving tackle attempt.