The 49ers promoted rookie offensive lineman Darrell Williams from the practice squad to the active roster Saturday and released veteran tackle Bryce Harris, whom they signed on Wednesday.
That means Williams won a three-day competition with Harris and will serve as the so-called swing tackle in Sunday's game. He'll back up both Trent Brown at left tackle as well as the right tackle, which will be either Zane Beadles or Erik Magnuson.
The 49ers did not use any of their draft picks on offensive linemen. Williams (6-5, 315) went undrafted out of Western Kentucky but played well during the offseason and preseason and landed on San Francisco's practice squad to start the season.