The San Francisco 49ers host the Houston Texans tonight for the third preseason game. Usually this means that the designated starters see extended playing time but the Niners have a new head coach and with it comes a new approach.

Jim Harbaugh said that he would bring in the backups early to give them the opportunity to play against starters. Quarterback Alex Smith will start tonight but could be replaced with Colin Kaepernick after two offensive series. Smith may return to the game if the situation permits. This could be for a two-minute drill or just another series.

Defensive coordinator Vic Fangio wants to play zone defense against the Texans, after focusing on the blitz last week. Donte Whitner is likely going to be the starter at strong safety once the regular season kicks off but Dashon Goldson and Madieu Williams are battling for the other safety spot.

The left cornerback competition seems settled. Carlos Rogers will be the starter with rookie Chris Culliver as his backup. There are still three players who hope to win the starter job on the right side, Shawntae Spencer, Tarell Brown and Tramaine Brock. Look for Brown and Brock to get plenty of opportunities tonight to make big plays.

First-round pick Aldon Smith is always under the scope and many expect him to become a starter soon. Smith won the first round at New Orleans Saints but Parys Haralson was the better ROLB against the Oakland Raiders. The battle appears to be tied at the moment, which works in Haralson’s favor, so expect Aldon Smith to see a lot of action tonight.

The 49ers are converting Bruce Miller from defensive end to fullback. It would be nice to see him block for Frank Gore tonight but the running back is going to leave the game early. Regardless, Bruce Miller will see a great deal of playing time against the Houston Texans.

Lastly, the center battle is a wide open race and will remain so even after tonight’s game. Offensive coordinator Greg Roman announced that both, Adam Snyder and Jonathan Goodwin, would see an equal amount of playing time against the Texans.

Tonight may only be another preseason game but San Francisco’s backups will be tested against Houston’s starters. Jim Harbaugh wants his twos and threes prepared for every situation that may occur in the regular season, and this includes playing against the best players on the opposing team.