I hate using this argument but if you look historically the raiders always play the chargers tough no matter how bad or good each team is. Last year the Raiders beat them twice as 7-10 point underdogs and they beat them at home by 15.
I think chargers is the right play but this game has backdoor written all over it. I would not put a huge wager on this. If anything i think the over is a better play because the defenses have not had enough time to game plan for this. Second half the defenses for both teams will be worn down with short rest and short prep time.
The fact Denver beat Oakland is sort of an anomaly. The Dolphins beat the Pats 38-13 in 2008 when they surprised them with the wildcat. Not a big surprise that Oakland was caught off guard by the option. Doesn't help against the option when your best LB, McClain, didn't play either.