The Falcons' coaching staff still believes that Williams, a second-round pick in 2006, and Houston, a second-rounder this year, have enough talent to become starting defensive backs.
For now, though, both players will serve the team better as reserves.
Coach Bobby Petrino wants Williams to close faster and hit harder. Williams, who's listed behind Chris Crocker at free safety, took most of the snaps in the preseason finale last week, a 13-10 victory over Baltimore.
On the Ravens' next-to-last drive, Williams recovered a fumble at the Baltimore 31.
"I thought Jimmy started to play more physical," Petrino said Monday. "He ran to the ball and made some of the tackles we're going to count on him making."
Because Petrino wanted to avoid injuries to all of his first-teamers, Williams started for Crocker and Houston for Lewis Sanders.
Both players took most of the snaps at their positions, and Petrino liked what he saw. Houston led the Falcons with eight tackles, and his interception of quarterback Troy Smith ended Baltimore's final possession.
"He was getting closer to the receivers," Petrino said. "He started to get in position to make plays on the ball, and that takes reps."
The Falcons return three starters - Crocker, left cornerback DeAngelo Hall and strong safety Lawyer Milloy - from a secondary that contributed last year to a No. 29 ranking against the pass.
"I played with DeAngelo in college, but this is a whole different level," Williams said.