Not going to beat anybody with four turnovers. Defense actually played decent for the majority of the game, but when they needed a stop, they couldn't get it.
Aside from Praeter being a somewhat decent kicker (30 yard shank today aside), the Broncos have to have, by far, the worst special teams in the league. Just getting the ball back to the 20 on a kickoff is a great return for Denver, and it's been that way for years, unfortunately. Meanwhile, on the other side of things, you just hold your breath and hope the other team doesn't break one, which happens a lot more often than it should.
Broncos had chances to pull away early, but the Marshall fumble went from driving to take a potential 14-6 lead to trailing 13-7. Broncos are lucky they have an easy schedule, because that's the only reason they may potentially make the playoffs.