The first drive, which opened the game, began auspiciously, with Ben Kelly returning the opening kickoff 36 yards and Rob Konrad taking a Jay Fiedler swing pass 25 yards to give Miami a first down at the Rams 34-yard line.
But Fiedler's next pass was thrown into traffic and was tipped into the air by linebacker Don Davis. Cornerback Dexter McCleon came down with the deflection to end the drive.
After Kenny Mixon stopped the Rams' first drive with a third-down sack, the Dolphins marched 70 yards on 11 plays to take a 7-0 lead.
The big plays in the drive were third-down completions by Fiedler of 16 yards to Konrad, 16 yards to Oronde Gadsden and 11 yards to tight end Jed Weaver.
Lamar Smith, who began the drive with a 10-yard run, capped it with a 2-yard touchdown run.
That was the end of the night for Smith, Fiedler and most of the first-team offensive line.
"Other than that interception, I thought the first offense did very good," Fiedler said. "Overall, it was a pretty good effort."
The Dolphins' first-team defense played without starters Tim Bowens (knee) and Patrick Surtain (knee), but faced a Rams offense that was without Pro Bowl running back Marshall Faulk and Pro Bowl wide receiver Isaac Bruce. In addition, Rams quarterback Kurt Warner played only one series and never attempted a pass.
St. Louis won the game when fourth-string quarterback hit tight end Jeff Robinson with a 3-yard touchdown pass early in the fourth quarter. The score was set up by a 30-yard pass interference call on Dolphins cornerback Deshone Mallard.
The Rams' scoring drive began at their own 43-yard line after Olindo Mare came up short on a 53-yard field goal attempt that would have given the Dolphins the lead.
As has been the case throughout training camp, injuries hit the Dolphins on Monday night.
In the first half alone, defensive end Jason Taylor (left shoulder), quarterback Ray Lucas (back strain) and running back J.J. Johnson (left knee) all went down with injuries.
Of the three, the only one that appeared potentially significant was the one suffered by Taylor.
"I'm fine. It's no big deal," Taylor said. "Hopefully, I'll be back at practice tomorrow."
Lucas was scheduled to play well into the third quarter, but his injury changed those plans. Mike Quinn, who might have to hold off rookie Josh Heupel for the No. 3 quarterback job, came into the game after the Rams had taken a 10-7 right after the two-minute warning.
Quinn, thanks to some nice plays by wide receiver James McKnight and running back Autry Denson, led the Dolphins on a field goal drive, with Olindo Mare hitting a 45-yard kick as time expired in the first half.
After the Dolphins' first-team offense had finished its work, St. Louis cut the lead to 7-3 on Jeff Wilkins' 34-yard field goal the next time it had the ball. Aveion Cason returned the kickoff 31 yards, and Mare's facemask penalty tacked on 15 yards, giving the Rams a first down at the Miami 39-yard line.
The Rams drove all the way to the Dolphins 11, but Lorenzo Bromell got a sack after quarterback Joe Germaine dropped the ball in the pocket and Zach Thomas knocked down a third-down pass to force St. Louis to settle for a field goal.
The Rams took the lead late in the second quarter after the Dolphins went for the first down on fourth-and-2 from the Rams 41-yard line and rookie Travis Minor was stopped for no gain.
The Rams needed 12 plays to drive 59 yards, the touchdown coming on Germaine's 2-yard draw on second-and-goal.