The Rams, who gave up 25.4 points per game last season, were supposed to be improved on defense with the arrival of corner Cortland Finnegan, tackle Kendall Langford and draft picks Michael Brockers and Janoris Jenkins.
The first half of Saturday’s game in Dallas showed how far the team has to go.
Jenkins, Finnegan, safety Craig Dahl and linebacker Rocky McIntosh all missed tackles as the Cowboys built a 17-3 lead. Running back DeMarco Murray converted third-and-10 on a dumpoff by juking three defenders. Backup wideout Dwayne Harris squeezed through Dahl and Jenkins for a 38-yard touchdown when he should have been pushed out of bounds.
"We're not tackling like we did the last couple weeks," coach Jeff Fisher said at halftime.
The team’s third-down woes deepened. Dallas converted three of five first downs in the first half, making Rams opponents 19 of 31 (61 percent) this preseason.
The rookie Jenkins had a particularly bad night, getting burned in the first quarter on Kevin Ogletree’s 25-yard reception and then on Harris’ 61-yard TD catch. Fisher blamed miscommunication for some of the secondary's problems.
Jenkins is penciled in as the starter opposite Cortland Finnegan. An elite talent out of North Alabama, Jenkins had been enjoying a terrific preseason until Saturday.
Bradford, offense stumble: QB Sam Bradford hit 6 of 17 throws for 64 yards, but there was plenty of blame to go around. His protection broke down repeatedly, and his receivers struggled to get open.
It was a big step back for a unit that clicked in last week’s win over Kansas City.
But it wasn't exactly a dress rehearsal. Running back Steven Jackson did not get a carry, coming in only for pass protection.
Greg “The Leg” keeps booming: Rookie kicker Greg Zuerlein improved to 4 for 4 this preseason by hitting first-half field goals of 55 and 52 yard field goals. He also had a 52-yarder last week against Kansas City.
The 24-year-old from Missouri Western State has alleviated any concerns about replacing Josh Brown.
Dahl scratched: Guard Harvey Dahl made the trip to Dallas but did not play due to an unknown infection. He was replaced by Bryan Mattison.
Pro Bowl center Scott Wells made his Rams debut after missing the first two games while rehabbing from knee surgery.
Get more Rams updates and analysis from Larry Hartstein @CBSSportsNFLSTL.