Gameday preview: Vikings at San Francisco

Ah, the third preseason game, in which starters will toil for a complete half. Coach Leslie Frazier said the first units also will start the third quarter. … MVP RB Adrian Peterson will see his first preseason action in the nationally televised game. … The Vikings are 0-2, with losses to Houston (27-13) and Buffalo (20-16). … WR Jarius Wright (concussion) and FB Jerome Felton (appendix) are key players who will sit out. … The roster must be pared to 75 players by Tuesday. … Assistant head coach Mike Singletary is a former 49ers coach. … Backup QB McLeod Bethel-Thompson was in camp with the Niners in 2011, and FB Rhett Ellison's father, Riki, played for the 49ers when they won three Super Bowls. … QB Christian Ponder is 6-for-14 in the preseason for 68 yards and a 28.3 rating. Matt Cassel is 16-for-27 for 241 yards and an 85.6 rating. … Rookie WR Cordarrelle Patterson, who leads the team with six catches, will see kickoff return action again.

The Super Bowl runners-up have no QB controversy this season, with Colin Kaepernick at the helm. There is a battle for backup, though. Seneca Wallace signed this week after projected No. 2 Colt McCoy struggled in the preseason. … Coach Jim Harbaugh said all five QBs — Scott Tolzien and rookie B.J. Daniels are the other two — will play Sunday night. … WR Anquan Boldin signed as a free agent after winning a Super Bowl with Baltimore, and will be extra important because Michael Crabtree (torn Achilles' tendon) was lost until November. …The 49ers last season had five first-team All-Pros — LBs Aldon Smith, NaVorro Bowman and Patrick Willis; S Dashon Goldson; and P Andy Lee. LB Ahmad Brooks and DL Justin Smith were second-teamers. … The Niners lost 10-6 to the Broncos and beat the Chiefs 15-13. … Former Gophers QB MarQueis Gray has one catch for 13 yards and is listed as the fourth-string TE.

CHRIS MILLER