6 takeaways from 49ers 21-20 preseason win over Broncos

Takeaway #3: The cornerback competition was not a bluff

whoEarlier this week, Kyle Shanahan's comments about Isaiah Oliver indicated that the free-agent signee was not a guaranteed starter. This followed a practice where Oliver was with the second-string and Ambry Thomas, whose had his own ups and downs as a 49ers cornerback, started outside, with Deommodore Lenoir at nickel.

This configuration continued on Sunday's game, and Thomas played adequately, but not good enough to solidify his starting position.

Behind him, Sam Womack III, who was the starting nickel last year before slowly phasing out, continued his strong play at outside corner. UFDA corner D'Shawn Jamison struggled a bit at nickel but has played well otherwise, and the competition seems to have only just amplified.

Takeaway #4: The backup offensive line is still a problem

Coming off an abysmal performance against the Raiders, the backup offensive line could only move forward from there. However, their performance against the Broncos continued to raise concerns about the depth behind the starters.

The 49ers offensive line allowed three sacks on Saturday, but the stream of pressure was constant. Though it's unfair to expect perfect play from backup offensive linemen, they simply did not play well enough for a second week in a row. Given the 49ers injury problems on the line, there's a lot at risk.