The San Francisco 49ers coach said the two rookies have won starting jobs along the team's offensive line just nine days into training camp.
The 49ers also will have a new starter at center after Eric Heitmann broke his left leg during practice Monday morning. Heitmann is expected to miss up to two months.
Davis, the No. 11 overall pick in the draft, will now work exclusively with the first-team offense at right tackle. Iupati, drafted six picks after Davis, has moved to first on the depth chart at left guard.
"Those guys showed us that they have the ability to step in and be able to do it," Singletary said. "If that's the case, we have to give them all the reps that we can possibly give them in order to do the job and be ready."
The 49ers this year became the third team in NFL history to draft two offensive linemen in the first round, and both will make their debuts in Sunday's preseason opener at Indianapolis.
Davis, who doesn't turn 21 until October, would become one of the youngest 49ers ever to start a regular-season opener if he remains in the lineup for San Francisco's Sept. 12 game at Seattle.
While Iupati has been running primarily with the first team since the first day of padded practices, Davis didn't move ahead of incumbent Adam Snyder until taking all the first-team reps Saturday.
"This is a confidence booster, but you've got to put everything into perspective," Davis said. "That's just the first step. That's not my main goal. I want to be the best player I can possibly be."
The 49ers experienced even more shuffling along the offensive line after David Baas moved to center in place of Heitmann, San Francisco's most effective and consistent offensive lineman in recent seasons. Heitmann fractured his left fibula while pulling out on a running play.
Heitmann has started every game at center the past three seasons. He started the first 14 games of 2006 before breaking his left tibia.
Baas, who started all 16 games last season at left guard, suffered a concussion on Aug. 2 and missed several days of practice. Iupati took his place and hasn't budged since.
Singletary said Baas will now be the top backup to Iupati and challenge veteran Tony Wragge for starting center duties. Wragge started two games at center for the 49ers after Heitmann was injured in 2006.
Baas played center as a senior at Michigan in 2004, when he was named Big Ten offensive lineman of the year.
"We just have to give Baas a chance to really see what he can do at the position," Singletary said.
Baas, who has 38 career starts at both guard positions, said he is focused on his new opportunity at center.
"I want to win just like everybody else," Baas said. "So I'm coming out here and competing, and if they want me to compete at center, that's what I'm gonna do. I can't sit here and complain about it. You have to move on, you have to be the best football player at whatever position you can, so that's what I'm doing. I just want to play."
The 49ers also conducted most of Monday's morning practice without starting left tackle Joe Staley, who left the session early because of neck spasms. Staley's status is day to day.
LB Martail Burnett suffered a knee injury during the morning session and was taken to the locker room on a cart. ... WR Josh Morgan suffered a jammed neck late in practice after he was hit by safety Dashon Goldson. ... Singletary pulled the plug on Monday's morning practice at least 20 minutes early because of injuries and sloppy play. "I've been anticipating this day," Singletary said. "This is a wall day, hump day. And you've got to work your way through that wall. And we didn't handle that very well today."