Five things to watch: 49ers at Chargers

Five things to watch when the San Francisco 49ers face the San Diego Chargers at Qualcomm Stadium:

1. The pregame inactive list.

49ers linebackers Takeo Spikes and Patrick Willis wore casts on their injured hands this week. They missed practice time.

There's a chance one or both could wind up on the inactive list San Francisco submits 90 minutes before kickoff. If they are active, their hand injuries could make it tougher for them to pick off passes or make tackles. Spikes has an interception in two of the 49ers' past three games.

Willis has a career-high five sacks. The 49ers value his ability to get pressure up the middle in addition to the more conventional skills he offers from play to play.

2. Alex Smith's patience.

The 49ers' Alex Smith has six touchdowns and no interceptions in his past three starts. He has eight touchdowns in the past three full games he has played.

The numbers are starting to add up. Smith now has a higher passer rating for the season than any quarterback in the division.

The momentum Smith has built recently could dissipate quickly against this San Diego defense, however.

The Chargers have shown they can frustrate even the NFL's best quarterbacks. Peyton Manning tossed four interceptions against them three weeks ago.

Opposing quarterbacks have 12 touchdowns, 13 interceptions and a 72.9 rating against San Diego. Only the Green Bay Packers have held opposing passers to a lower overall rating (68.1).

3. The Pro Bowl tight ends.

The Chargers will probably play without Antonio Gates, leaving the 49ers' Vernon Davis as the last Pro Bowl tight end standing in this matchup.

Davis has caught a touchdown pass in the past five games Alex Smith has started. He has scoring receptions of 66 and 42 yards in his past two games.

Colts tight end Jacob Tamme caught seven passes for 64 yards and a touchdown against San Diego.

4. Those fiery halftime speeches.

The 49ers have scored only 30 points in third quarters this season, less than half what they've scored in any other quarter this season.

San Francisco has failed to score at all in eight third quarters. The 49ers haven't scored a third-quarter offensive touchdown since Michael Crabtree's 32-yarder against Oakland way back in Week 6.

San Diego has outscored its past six opponents 37-3 in third quarters.

Chargers coach Norv Turner isn't the fiery type. Halftime adjustments apparently trump halftime speeches.

5. Watch out for the long ball

Chargers quarterback Philip Rivers ranks second to Drew Brees in touchdown passes that traveled more than 20 yards in the air, ESPN Stats & Information notes.

The 49ers' defense has allowed 56.8 percent completions, by far the worst percentage in the league, on passes traveling at least that far.

Rivers has eight touchdowns, four interceptions and a 93.8 rating on these passes. He has completed 45.5 percent while averaging 17.0 yards per attempt. The 49ers have alloweed 21.2 yards per attempt with four touchdowns, two interceptions and a 115.0 rating on these throws.