49ers defensive coordinator Vic Fangio met with the media on Tuesday, and he revealed a pair of defensive starters for Thursday's preseason opener against the Denver Broncos. Demarcus Dobbs will get the start at right defensive tackle in place of Justin Smith, and Craig Dahl will get the start at free safety.
Eric Reid has been taking first team snaps at free safety, but Fangio has emphasized that the position involves a rotation between Reid, Dahl, Spillman, and I believe Trenton Robinson. There is no word on how the rotation will play on Thursday after Dahl starts the game.
Justin Smith is dealing with an apparent finger injury, and has missed a few practices over the last week. Demarcus Dobbs has been taking first-team snaps in place of Smith, so it is only natural that he will get the start in Smith's place. Dobbs has focused on special teams the last two seasons, but he has impressed on the line the last two preseasons.
Justin Smith and Ray McDonald have played the vast majority of snaps, and this has kept Dobbs on the sideline. The 49ers added Tank Carradine in this year's draft, but he is still rehabbing his November 2012 ACL tear and remains on the NFI list. Dobbs appears to have the edge for that extra defensive end spot, although Glenn Dorsey could very well work his way into the rotation. If Ian Williams gets the starting nose tackle job, Dorsey would likely join Dobbs as a key reserve along the line.