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ARLINGTON, Texas -- Tony Romo didn't need much time or his top three pass-catchers to show he's ready for the regular season.

Playing only a quarter in what was supposed to be his most extensive action of the preseason, Romo threw for 198 yards with two long touchdowns to Dwayne Harris, who got behind defenders and went through them to score in the Dallas Cowboys' 20-19 victory over the St. Louis Rams on Saturday night.

"Tony is an outstanding player and he's done it with a lot of different kinds of guys," coach Jason Garrett said. "It's nice to see him play well and play in a good rhythm with the younger guys."

Even with a preseason game left to play, Dallas (2-1) is already starting to turn its attention to the regular-season opener Sept. 5 at the defending Super Bowl champion Giants. Romo isn't expecting to play at home against Miami on Wednesday night, a week before that game in New York.

"I do know I've been preparing for New York for a while," Romo said. "We'll just get back to studying on them and take it from there."

The Cowboys are confident receivers Miles Austin (hamstring) and Dez Bryant (right knee tendinitis) will be ready to play against the Giants. Seven-time Pro Bowl tight end Jason Witten, who sustained a lacerated spleen in the preseason opener nearly two weeks ago, is uncertain.

Their absence wasn't an issue against the Rams (1-2), who lost 34-7 at Cowboys Stadium last October and have been inconsistent this preseason under new coach Jeff Fisher.

Romo completed 9 of 13 passes while playing three series, pushing the Cowboys to a 17-3 lead.

Harris finished with three catches for 118 yards and Kevin Ogletree, going into his fourth season, caught five passes for 75 yards.

"Injuries provide opportunity. With Dez and Miles being out, those guys have gotten more of an opportunity than they would have otherwise," Garrett said. "I think they've taken advantage of it."

Kyle Orton was 9 of 12 for 99 yards playing both series in the second quarter.

Harris, a sixth-round pick last year now in the mix to be the No. 3 receiver after Austin and Bryant, got behind the Rams' secondary for a 61-yard TD that put Dallas up 10-0 less than 9 minutes into the game.

On the next Cowboys possession, after Greg Zuerlein kicked the first of two field goals longer than 50 yards for St. Louis, Harris caught a pass coming across the middle of the field.

When Harris got close to the left sideline, where it looked like he might go out of bounds or get tackled, he instead split defensive backs. Craig Dahl and Janoris Jenkins ran into each other instead of the receiver near the 15, and Harris sprinted up the sideline to finish a 38-yard score.

"Jenks lost his footing on the first ball down the sideline. We had a communication problem on the long TD pass. Those things I'm not concerned about because they're correctable," Fisher said. "We gave up way too much through the air."

DeMarco Murray, who set a Cowboys' single-game record with 253 yards rushing against the Rams in his first start last season, had five carries for 26 yards and caught four passes for 16 yards.

On the Cowboys' opening 13-play drive, Murray converted third-and-10 when Romo scrambled out of trouble and dumped the pass to the running back, who made a quick move around two defenders. But Dallas had to settle for Dan Bailey's 38-yard field goal after Ogletree let a ball go through his hands on a third-and-6 play.

Sam Bradford played the entire first half for the Rams, and was 6-of-17 passing for 64 yards. He was sacked twice and under pressure plenty of other times.

The Rams had only 114 total yards before halftime, a week after scoring TDs on their first two drives against Kansas City in a 31-17 win. St. Louis lost 38-3 at Indianapolis in its preseason opener.

"Today was probably our worst performance in the three games. ... We're still pretty vanilla," Bradford said. "I don't think it was anything major. I think it's just getting some of the smaller details cleaned up."

Running back Steven Jackson started but never touched the ball, as was the plan.

St. Louis plays at home against Baltimore in its final preseason game Thursday, when Fisher plans to use Jackson and the rest of his starters extensively.

Even with a fake punt for a 30-yard gain and an offside penalty that got the Rams inside the 10, they didn't score when Bradford had consecutive incompletions from the 5. That included fourth down when Fisher opted against a chip-shot field goal for Zuerlein, who made kicks of 55 and 52 yards.

Cowboys safety Danny McCray sustained a strained neck on that fourth-down play when he ran into one of his own teammates. Nose Jay Ratliff sustained an ankle injury, and will be evaluated further Sunday.

Bailey kicked a 31-yard field goal at the end of the first half for a 20-6 lead after Harris had a 19-yard catch and Ogletree a 15-yarder.

Kellen Clemens threw a 2-yard TD to Austin Pettis in the fourth quarter for the Rams before a missed extra point. Chase Reynolds ran for a 4-yard score.

New center Scott Wells and receiver Brandon Gibson made their preseason debuts for St. Louis. Gibson had one catch for 14 yards, on the Rams' first offensive snap.