When offensive guard Kendall Simmons limped off the field in the Monday night game against the Baltimore Ravens and was lost for the season, an undrafted lineman was thrown into the breach as the Steelers rallied in the second half.

Then, with the running backs banged up and the offensive line still ailing in a Sunday night game at Jacksonville, that same unheralded player made his first NFL start and delivered again.

Little wonder, then, that Darnell Stapleton will get his second start at right guard Sunday against the Bengals in Cincinnati.

"He hasn't surprised me. Since he first got here, he's been a good football player," offensive coordinator Bruce Arians said after an indoor practice yesterday. "He's a very bright guy. Bright guys have a way of making things happen for the good. I think guys around him already appreciate him."

Stapleton was signed as a free agent out of Rutgers after the 2007 draft. He made the 53-man roster out of training camp as a center and guard. After being inactive for all the regular-season games, he dressed for the playoff game against Jacksonville but did not play. This season, he made his NFL debut as a reserve lineman and a contributor on special teams against the Houston Texans, and now he is the starting right guard.

Has it all sunk in yet?

"No, not really," Stapleton said, with a grin. "It's an opportunity of a lifetime. You have to be ready. I'm just trying to do my best to help the team. I'm just having fun. I just want to step in and deliver for my teammates."

Offensive linemen are a bit like middle relievers in baseball. Nobody knows their names unless something goes wrong or they get injured. Laboring in anonymity is part of the job description.

Rutgers wasn't exactly known as the short path to the NFL, either. But, as a senior, Stapleton was the starting center on a line that allowed just eight sacks, the fewest in the nation, while helping to spring running back Ray Rice for 1,794 yards.

"It probably shocks a lot of people on the outside when they think of NFL players from Rutgers," he said.

Not that he was lacking in confidence, but his play against the Ravens gave him a comfort level that he carried into the game against the Jaguars. The prime-time spotlight didn't faze him at all.

"You can't go out there scared or you could get somebody hurt," Stapleton said. "We had a good outing in Jacksonville. We want to build on that and move forward. Hard work is paying off. But there's stuff I still have to learn."

What was most remarkable in Jacksonville was that the Steelers were down to their third-string running back in Mewelde Moore, with practice-teamer Gary Russell and Najeh Davenport in reserve. Then, Moore rushed for 99 yards to balance the attack.

"They got it done up front," Moore said.

The offensive line was a noted question mark this season with the departure of Alan Faneca and the arrival of new center Justin Hartwig. But Stapleton, a strong worker in the offseason, showed enough promise and added enough depth to make Sean Mahan expendable in a trade.

The depth is being sorely tested, but, based on the last two games, coach Mike Tomlin didn't have to think too hard in staying with Stapleton against the Bengals.

"When you think about the six quarters he's played, you measure his performance because we've been effective as an offense.

"We played a half of winning football against the Ravens when he was in there. And we played a game of winning football against Jacksonville when he was in there. He's more than held his own," Tomlin said.

"He's a pretty good communicator. Guys seem to have a level of comfort with him. Of course, he's going to continue to get better with reps. That's our hope."

The Steelers liked what they saw in Stapleton for several reasons. He had the flexibility to play center and guard. He learned the offense quickly. And he wasn't awed about getting thrown into the fire.

"He appears to be a quick study. He doesn't make the same mistakes repeatedly. If he makes mistakes, they're new mistakes," Tomlin said. "Those things keep us coming back to him and keep him hanging around. And when given an opportunity, he's seized it."