By Tony Moss, NFL Editor -- (Sports Network) - With all of the major position battles more or less won for the San Francisco 49ers and San Diego Chargers, Friday's final preseason game at Candlestick Park will be about avoiding injuries and determining a couple of spots near the bottom of both rosters.

The Niners and Bolts will have roughly 15 hours following the completion of Friday's game to whittle their active rosters from 75 to 53 players.

The biggest suspense of August in 49ers camp was related to the quarterback battle, but that was settled when head coach Mike Nolan named journeyman J.T. O'Sullivan as the team's starter for the regular season opener against Arizona on Sept. 7th.

Former No. 1 overall Alex Smith appears resigned to backup status, and part- time 2007 signal-caller Shaun Hill will hold the clipboard, if he makes the squad at all.

Whoever takes the snaps on Friday could be playing with an offense that includes guard David Baas and wide receiver Bryant Johnson for the first time this preseason.

Baas, an oft-injured former second-round Draft choice of the Niners, underwent offseason surgery to repair a torn pectoral. Johnson, a free agent acquisition formerly with the Cardinals, has been dealing with a hamstring strain.

The Chargers figure to take a decidedly hands-off approach to Friday's warm- up.

The team has already held All-Pro running back LaDainian Tomlinson out of all its preseason games to date, and with outside linebacker Shawne Merriman (knee) possibly out for the year and tight end Antonio Gates (foot) still recovering from offseason surgery, San Diego can ill-afford any more injuries.

Also likely factoring in to the limitation of playing time for the Chargers is that the team will be working on just three days rest after defeating the Seahawks, 18-17, on Monday in Seattle.

Norv Turner's squad opens the regular season on Sept. 7, at home against the Carolina Panthers.

The all-time preseason series with the Chargers and 49ers is deadlocked, 18-18, with San Diego tying the series by virtue of a 16-13 home victory prior to last season.

The most memorable game played between the two franchises was Super Bowl XXIX, won by the Niners, 49-26.