ST. LOUIS -- The Pittsburgh Steelers won a game but lost a quarterback, at least for the time being, after defeating the St. Louis Rams 12-6.

Steelers quarterback Ben Roethlisberger was knocked out of the game with a left knee injury with 5:35 remaining in third quarter. Rams safety Mark Barron was blocked and rolled into Roethlisberger's leg on a sack. Roethlisberger was on the turf for several minutes before limping off the field.

Steelers head coach Mike Tomlin had little information on Roethlisberger, except to say he was "being evaluated" and would have an MRI after returning to Pittsburgh. When pressed if there were any X-rays or anything more, Tomlin said he didn't have anything more, and added, "I promise I'll give you more when I have it."

Before leaving the game, Roethlisberger completed 20 of 24 passes for 192 yards with an interception. He had entered the game needing 223 yards to reach 40,000 for his career.

"This was a good, tough ballgame," Tomlin said. "It's good to come out on top of those. ... We have to be able to go on the road in a hostile environment be able to win. We can check those two things off today and hopefully we can grow from it."

When it was noted the large Steelers contingent in the crowd that forced the Rams to go to a silent count in the red zone meaning it wasn't that hostile, Tomlin smiled and said, "The Rams' front had something to do with it being hostile. It might not necessarily mean the fans. It might just mean how they were playing. I have a lot of respect for those guys and knew it going in."

That defense sacked Roethlisberger and backup Mike Vick five times, and limited running back Le'Veon Bell to 62 yards on 19 carries. Bell was playing his first game of the season after missing the first two under league suspension.

For the Rams, following an opening-week 34-31 overtime win over Seattle, they have lost to Washington and Pittsburgh while scoring a total of 16 points and one touchdown.

Head coach Jeff Fisher stated simply, "Six points isn't going to win you a whole lot of games."

Added quarterback Nick Foles, "We weren't good on third down and we have to get the ball in the end zone. We're just not getting it done."

The Steelers took an early 3-0 lead with 7:18 to play in the first quarter on a 21-yard field goal by Josh Scobee after they drove almost effortlessly from their own 20-yard line to the Rams' 10 on the opening possession of the game. Roethlisberger completed 7 of 8 passes for 71 yards in the drive. The Rams' defense stiffened after tight end Heath Miller caught a first-and-goal pass at the 2-yard line. However, defensive Robert Quinn deflected a second-down pass, and running Bell was dropped for a 1-yard loss on third down.

They extended the lead to 9-0 when Bell capped a 12-play, 92-yard drive with a 1-yard touchdown run. A Roethlisberger pass on a 2-point conversion try was broken up by cornerback Trumaine Johnson.

The Rams got on the scoreboard with a 49-yard field goal by Greg Zuerlein with 2:05 remaining in the second quarter to make it 9-3 at halftime.

There was no scoring in the second half until Zuerlein kicked a 27-yard field goal with 5:38 remaining in the fourth quarter. The Rams had advanced to the Pittsburgh 7-yard line following a 31-yard pass interference penalty on cornerback Antwon Blake and a 24-yard run on a quick handoff to wide receiver Chris Givens. However, a 2-yard loss by running back Tre Mason, followed by two false starts with that loud pro-Steelers crowd and an incomplete pass, pushed the ball back to the 19-yard line where Foles ran 10 yards on third down.

The Rams held Pittsburgh to 72 yards in the second half and had two opportunities to take the lead after Zuerlein's field goal.

With 3:02 left in the game, Foles overthrew tight end Lance Kendricks on a seam route and the pass was intercepted by safety Will Allen. He returned it to the Rams' 31-yard line, and the Steelers settled for a 41-yard field goal by Scobee.

The Rams started their final drive on their own 21-yard line and after one first down, the drive stalled. However, on fourth-and-5, officials ruled wide receiver Kenny Britt had caught a Foles pass that would have been good for a first down at the 46-yard line with 1:15 remaining. However, the play was reversed on review, with the officials ruling Britt failed to maintain control throughout the catch.

"I thought it was catch," Britt said. "But I don't make the calls."

NOTES: Rams LB James Laurinaitis had two tackles in Pittsburgh's first possession to become the franchise's all-time leading tackler. He passed Hall of Fame DT Merlin Olsen, who amassed 915 tackles in his career. According to press-box statistics, Laurinaitis had eight tackles in the game to give him 922 for his career. ... Steelers ILB Ryan Shazier, who injured his shoulder in the previous week's game against the San Francisco 49ers, was inactive. ... RB Todd Gurley made his debut for the Rams after being inactive for the first two games of the season. The 10th overall pick in the draft, Gurley had suffered a torn ACL on Nov. 15, 2014, while playing for Georgia against Auburn. He had six carries for nine yards in the game and caught one pass for five yards. ... QB Mike Vick replaced Ben Roethlisberger and completed 5 of 6 passes for 38 yards. ... The game was delayed 26 minutes because of a pyrotechnic cart malfunction during pregame introductions that resulted in the turf catching fire briefly. The fire was quickly extinguished, but the delay occurred while residue was cleaned from the area around the 3-yard line about 25 feet from the Rams' sideline.