Three things: Broncos-49ers

Three things to watch for Thursday night in the San Francisco 49ers' 2013 exhibition opener against the Denver Broncos at Candlestick Park (9 p.m. ET):

1. Young receivers. A.J. Jenkins will be looking to shake Denver's defensive backs and perceptions of him as a disappointing 2012 first-round draft choice. Jenkins generally enjoyed a constructive offseason until a hamstring injury caused him to miss practice time this summer. Jenkins returned to practice this week and quickly made an impact with his speed. He should get an extended look against the Broncos and a few chances to catch passes from multiple quarterbacks. Quinton Patton, Ricardo Lockette and Marlon Moore are also among the young receivers with something to gain.

2. Secondary dynamics. Tramaine Brock appears to have the inside track against Nnamdi Asomugha in the race to become the 49ers' third cornerback. Their competition will be one to watch. In the bigger picture, it's telling that a three-time Pro bowl choice such as Asomugha is struggling to beat out an undrafted fourth-year player from Belhaven with no more than 86 defensive snaps in a season. We'll also want to keep an eye out for rookie Eric Reid and the other players challenging for the starting job at free safety. Reid has been looking forward to making his NFL debut against Peyton Manning, but veteran Craig Dahl appears more likely to start at free safety in this game.

3. Backup QBs. Colt McCoy heads into the exhibition season as the 49ers' likely No. 2 quarterback behind starter Colin Kaepernick, who will not play much in this game. Scott Tolzien and B.J. Daniels are also competing for that No. 2 job. A rough outing from McCoy or a particularly strong outing from one of the others could shake up the competition.