He also recorded eight tackles and a game-high three pass deflections.
"Corey Graham came up big," Ravens coach John Harbaugh said. "He played really well."
Added Graham: "That's how it is. When you have injuries, the next guy has to step up and I was fortunate enough to get the opportunity to play with Ed Reed and Chykie Brown and you just got to step up and make plays. The game's not going to stop, and the team's not going to stop. We have to find a way to fit in and find a way to get it done."
The Pro Bowl special teams ace also delivered a big hit on unsuspecting Steelers tight end Heath Miller late in the game to help preserve the win.
"I tried to go out there and make plays, and I was fortunate," said Graham, who intercepted three passes last season with the Chicago Bears before signing a two-year contract with the Ravens in March. "He didn't see me coming and instead of going for the ball, I went for the hit."
Meanwhile, backup safety James Ihedigbo delivered a punishing hit on his sack of Leftwich on a delay blitz.
"It was a zone pressure," Ihedigbo said. "I was supposed to come outside, and I saw it open up. A window opened up and I went for the kill. I went for it and made a good play. That's what I'm here for, whatever I can do to make an impact. I was glad that I did and helped our team."
The Ravens' oft-maligned defense held the Steelers to 10 points as Leftwich completed just 18 of 39 passes for 201 yards and no touchdowns for a 51.3 quarterback rating.
The Steelers were held to 17 first downs and 311 yards of total offense, progress for a defense that has struggled to stop people this season.
"We got to find a way to go out there and get it done," Graham said. "We haven't been playing the best the last couple weeks, or the whole season some people say, but we have to find a way to get wins and that's what we were able to go out and do today."