From the unparalleled Michael Lombardi talking about the Denver Broncos:
"They’re for real — and last night proved it to me. I’ve always been concerned about their age and lack of real speed in the secondary, but after playing well the past two weeks against some very good passing teams, I’m a believer. Not allowing the Chargers a third-down conversion in the second half was impressive, as is giving up only three points in the second half all season. This is the fourth consecutive game their defense has held an opponent to zero third-down conversions (0/23) in the second half. The Broncos have allowed only two second-half third-down conversions this season (one each in Week 1 and Week 2). These numbers are a credit to their defensive staff for being able to make the right halftime adjustments. And as we all know, football is a game of adjustments."
Three straight games without allowing a third down conversion explains everything. 6-0 is not an accident.