ST. LOUIS -- Ben Roethlisberger stayed down a long time, needed plenty of help getting off the field and finally was carted off with a left knee injury.

The Pittsburgh Steelers needed their defense to step up without a quarterback who has been hard to knock out, holding off the St. Louis Rams 12-6 on Sunday.

Le'Veon Bell scored from a yard out in the first half in his first game back after a suspension, but the Steelers' focus will be on the status of their star quarterback.

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Will Allen's interception with 1:56 left set up a field goal by Josh Scobee to put Pittsburgh ahead by six points.

Pittsburgh (2-1) averaged 32 points in its first two games but was held down well before Roethlisberger's leg got caught underneath him on a diving, sliding sack by Mark Barron.

The Rams (1-2) were limited to two field goals by Greg Zuerlein and have scored just 16 points the last two games. Their last chance ended when the Steelers successfully challenged a potential first-down catch by Kenny Britt near midfield with 1:19 to play.

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

There was no immediate word on the extent of Roethlisberger's injury.

Backup Michael Vick was 5 of 6 for 38 yards and had two carries for minus-2 yards.

Attendance of 52,433 included thousands of Pittsburgh faithful that still left the Edward Jones Dome more than 13,000 shy of capacity.

Antonio Brown had 11 catches for 108 yards, his third straight 100-yard receiving game.

Both teams had running backs make debuts and Bell's production was far superior to that of Rams rookie Todd Gurley.

Bell had 62 yards on 19 carries. Gurley, who did not start and split time with Tre Mason, had just 9 yards on six carries.

Scobee's short field goal and a 1-yard run by Bell put Pittsburgh up 9-0 early, although it failed on the 2-point conversion for the first time in four chances when Roethlisberger threw incomplete.

The Steelers were fooled on a fake punt at midfield in the second quarter but Stedman Bailey couldn't scoop Johnny Hekker's underthrown ball before it hit the turf.

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 between the 3 and 4-yard line.