ST. LOUIS (AP) Ben Roethlisberger left the Edward Jones Dome on crutches.

Beating the St. Louis Rams 12-6 on Sunday proved costly for the Pittsburgh Steelers, who lost Big Ben with a left knee injury.

''I've never seen him down, so it was a little shocking,'' wide receiver Antonio Brown said.

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The Steelers scheduled an MRI Monday for Roethlisberger, who was injured on a diving, sliding sack by Mark Barron in the third quarter.

''He is being evaluated, I gave you all the information I have,'' coach Mike Tomlin said. ''I promise I will give you some more when we get it.''

Teammates on both sides of the ball know they've got to step up in the meantime.

Pittsburgh's offense, which averaged 32 points over its first two games, was struggling before Roethlisberger was hurt.

Roethlisberger hasn't missed a game since late in 2012, and this was his franchise-record 108th victory, passing Hall of Famer Terry Bradshaw. He was 20 of 24 for 192 yards and an interception.

Le'Veon Bell scored from a yard out in the first half, but the Steelers needed their defense most.

''You grow infinitely when you pull those out,'' Tomlin said. ''Obviously not the type of game we're searching for, but a win nonetheless.''

Other observations from Steelers vs. Rams:

BACKUP PLAYS: Michael Vick was caretaker for the Pittsburgh offense, going 5 of 6 for 38 yards with two carries for minus-2 yards. He signed a one-year deal in late August and is still learning the offense.

''He got us out of the stadium,'' Tomlin said. ''That is what the backup quarterback's job is.''

BACKS DEBUT: Bell and Rams rookie Todd Gurley both played for the first time this year. Bell was coming off a two-game suspension, and Gurley coming off left knee surgery last November while still at Georgia. The Steelers All-Pro had the better day with 62 yards rushing and 70 receiving. Gurley didn't start and split time with Tre Mason, gaining 9 yards on six carries with one reception for 5 yards.

''It's the first game. I've got to get in the groove of things,'' said Gurley, the 10th overall pick in the draft.

KEY STOPS: The Steelers held the Rams to 2 for 10 on third down and 0 for 2 on fourth and allowed just two field goals by Greg Zuerlein. Will Allen's interception with 1:56 left set up a field goal by Josh Scobee to put Pittsburgh ahead by six points.

''Fourth quarter picks are great,'' Allen said. ''Lawrence Timmons did a great job of causing a hot throw and I was just in position.''

BIG CATCHES: Antonio Brown had 11 catches for 108 yards, his third straight 100-yard receiving game. Nine of them came in the first half, tying the franchise record set by Hines Ward in the second half against Cincinnati on Nov. 30, 2003. He extended his NFL record to 21 consecutive games with at least five receptions and 70 yards.

LOW PRODUCTION: The Rams have totaled 16 points the last two games, plagued by dropped passes, penalties and all-around ineffectiveness. Kenny Britt was the lone offensive standout Sunday with seven catches for 102 yards.

''We're 1-2, the world's not ending,'' quarterback Nick Foles said. ''We will figure it out.''

WELL-TRAVELED: Attendance of 52,433 included thousands of Pittsburgh faithful waving Terrible Towels and disrupting the Rams offense enough that Foles had to go to a silent count at times. Even with the boost provided by Steelers fans, the Edward Jones Dome was more than 13,000 shy of capacity.

BURN UNIT: Kickoff was delayed about 26 minutes by a small fire near a corner of the south end zone from sparks emitted by a pyrotechnic display during Rams player introductions. The cleanup job was hampered by a malfunctioning wet-dry vacuum that spewed collective material back out. Neither team made any plays near a circular mark left between the 3- and 4-yard line.

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