The Denver Broncos' final result Sunday -- a 29-24 loss to the 49ers -- can be laid entirely at the feet of the backups.

After Peyton Manning left the game, the Broncos began mixing reserves into the first team, replacing Manning with Caleb Hanie and inserting RBs Knowshon Moreno and Jeremiah Johnson and WR Matt Willis for extended periods. But the offense kept going, overcoming a Hanie interception on the first play of the quarter and eventually cobbling together a 12-play, 73-yard drive at the end of the half that culminated in a 5-yard Hanie-to-Joel Dreessen touchdown.

But in the second half everything broke down. For the second consecutive game, the Broncos were shut out in the backups-vs.-backups portion of the game, as the 49ers scored all 19 second-half points. Combined with the previous week's loss to Seattle, Denver's second- and third-teamers have been outscored 40-0.

"It all concerns me. That's kind of what I do," Fox said. "I think at the end of the day, we made a little bit of improvement. Not a lot, but last week we (allowed) 21 (points)."

Just like last week, rookie QB Brock Osweiler took the field for the second half. Protection quickly broke down and he found himself under duress -- just like last week.

"The second unit, we've just made a small mistake here, a small mistake there, a penalty, a bad drop, a bad throw, a bad read," said Osweiler.

There were glimmers amid the second-half gloom for the Broncos. Their defense turned stout in the red zone, holding the 49ers to two field goals on their two second-half forays inside the 20-yard-line. Osweiler wasn't sacked and successfully escaped pressure multiple times.

"For me to have to step up in the pocket while I'm getting pressure and keep my eyes downfield, every time I can get that in the preseason, that's only going to make me better as a quarterback in the future," Osweiler said.

Banged up: RB Lance Ball suffered a rib injury when he landed after catching a 38-yard pass from Peyton Manning in the first quarter, but didn't consider it serious.

"If it was a regular-season game, I'd have been out there," Ball said. 

Rookie CB Omar Bolden left because of a bruised knee. He had been working on kickoff returns, but had no chance to show his skills because all of the kickoffs he was set to field sailed into or out of the end zone for touchbacks.

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