The visitors held their ground throughout the opening period and their positioning paid off once more before the end of the first quarter.
Danny Trevathan stole in to secure a 25-yard interception return in order to give his side a 14-0 lead, with the boot of McManus adding another point.
With just over five minutes remaining in the second offering, McManus returned once more to notch an impressive 23-yard field goal in order to push Denver into a healthy advantage.
The Chargers threw themselves a lifeline just before the whistle, with Josh Lambo producing something special from all of 51 yards to take the scores to 17-3 at the interval.
The hosts looked the stronger side for much of the third quarter, but Denver's relentless pressure on quarterback Philip Rivers negated much of San Diego's threat.
The fourth quarter proved much of the same as neither side could add to what they scored in the first half.