That image above, of Philip Rivers throwing a pass about 2 seconds after it should've been thrown and paying for it with an interception that was returned for a defensive touchdown by the Denver Broncos, is all you really need to know about the game.
The Chargers got off to a 24-0 lead, which was the score at half-time, by taking advantage of mistakes. The Broncos fumbled a punt return (which turned into a FG) and then a kickoff (which turned into a TD) before Manning hit Quentin Jammer in the chest with a pass that he ran back for a touchdown of his own. Halftime was fun for the Bolts and their fans. The blowout was on.
Then, the second half happened, and Peyton Manning turned in a flawless half of football while Philip Rivers became Matt Cassel. Rivers finished with 6 turnovers (4 interceptions, 2 fumbles) for the game, 5 coming in the second half. He was inaccurate, he held on to the ball too long, he made poor decisions and he generally looked like a QB that would prevent his team from winning any football game. That's how the Broncos ended up scoring 35 unanswered points.
The San Diego Chargers needed this win, after losing in spectacular fashion to the New Orleans Saints last week, to prove to everyone that they were for real. What they ended up proving is that they can't do much of anything besides stop the run, and it has become a well-known fact that if you sell-out against the Chargers running offense that Philip Rivers will eventually gift you with a turnover (or 6) to get your back in the game.
What a terrible night for the Chargers, their coaches, their players, their fans and anyone that was hoping that Philip Rivers' mistakes in 2011 were just a temporary thing. They were/are not. They are a very real problem that is still undefined and, therefore, unfixable in the foreseeable future. It is what it is.