ST. LOUIS — With assistance from the Dallas Cowboys defense, Tony Romo’s fourth quarter this week featured a comeback win instead of the meltdown many expect.

The Cowboys quarterback’s 12-yard touchdown toss to wide receiver Terrance Williams with 6:13 remaining capped the Dallas comeback from a 21-point first-half hole in a 34-31 win over the St. Louis Rams at the Edward Jones Dome on Sunday.

Linebacker Bruce Carter, who missed time in the third quarter with a head injury, applied the clincher by returning an interception 25 yards for a score at the 5:58 mark.

Romo finished 18 of 23 for 217 yards and two scores as Dallas opened its fourth consecutive season with a 2-1 mark. Running back DeMarco Murray, who rushed for 428 yards in his first two cracks at the Rams, collected 100 yards on 24 attempts.

St. Louis (1-2) got a good game from backup quarterback Austin Davis, other than his ill-advised pass over the middle that Carter pilfered. Davis, making his second start for the injured Shaun Hill (thigh), hit 30 of 42 attempts for 327 yards and three touchdowns.

Davis hit wide receiver Austin Pettis with a 4-yard scoring strike at the 2:36 mark, putting the Rams within three points. But Davis’ bid at a game-tying or winning drive died when cornerback Morris Claiborne picked him off at the Cowboys’ 42 with 1:02 remaining.

St. Louis’ offense had its way early. It opened the game with a 15-play, 80-yard touchdown drive that melted 8:50 off the clock, scoring on a 1-yard pass from Davis to tight end Lance Kendricks.

After forcing and recovering a fumble by Murray on their 35, the Rams scored five plays later. Davis hit wide receiver Brian Quick for a 51-yard touchdown on the second quarter’s first play.

St. Louis’ defense got in on the act at the 6:06 mark when cornerback Janoris Jenkins picked a Romo pass and high-stepped 25 yards for a score, making it 21-0.

Dallas got back into the game with two scores in the final 2:07 of the half. Murray plunged over from a yard, and a botched center snap by the Rams set up the Cowboys at their 47. Kicker Dan Bailey drilled a 29-yard field goal with two seconds remaining to make the score 21-10 at halftime.

Romo started the second half with a 68-yard scoring strike to wide receiver Dez Bryant, who got at least 10 yards behind any defender because of play-action and a coverage breakdown. That cut the St. Louis lead to 21-17 at 12:48 of the third.

Bailey converted a 40-yard field goal with 2:43 remaining in the third, but the Rams responded with a 28-yard field goal from kicker Greg Zuerlein with 13:28 left in the game.

NOTES: St. Louis WR Tavon Austin (knee), who was injured in the second quarter of last week’s win in Tampa Bay, was the team’s most notable inactive. … Dallas declared starting MLB Rolando McClain (groin) and LB Justin Durant (groin) inactive. … The Rams entered Sunday with 106 sacks since the start of the 2012 season, the most in the NFL. But they managed just one in this season’s first two games.