Pittsburgh ? Their right guard went down early in training camp, and their inside linebacker followed shortly after that. The veteran quarterback joined the injury list two games into the season, and their Pro Bowl nose tackle, top cornerback and best running back followed.

So many injuries for the Pittsburgh Steelers (9-1), all at positions where an inexperienced backup’s mistake can ruin a game — or a season. So how are they managing not only to overcome the injuries, but to go on an eight-game winning streak?

Just call it a series of well-timed coincidences — of astute offseason decisions coupled with a timely draft day move — plus the expectation that backups will raise their level of play once they are needed.

“When you talk about the chemistry on a football team, a lot of times it’s not so much the starters, it’s the whole mix,” coach Bill Cowher said. “It’s the guys who are able to accept roles and embrace them. No one has dwelled in self-pity and said, ‘Oh, woe is me.’ Each guy has been held accountable.”

Jerome Bettis began the season as the NFL’s No. 6 career rusher, yet agreed to cut his salary from $3.6 million to $1 million and remain as a backup after the Steelers signed free agent Duce Staley. So when Staley went down because of a bruised hamstring, Bettis stepped in with three consecutive 100-yard games — the first time he’s done that since 2001.

“Look at how well he’s doing,” offensive coordinator Ken Whisenhunt said. “He’s had some injuries the last couple of years, and he looks like a young man out there.”

Staley is expected to return Sunday against the Redskins.

And if director of football operations Kevin Colbert and Cowher hadn’t drafted Ben Roethlisberger — the only quarterback Pittsburgh has taken in the first round in 24 years — they might have been left scanning the waiver wire when starter Tommy Maddox and backup Charlie Batch were hurt.

Instead, Roethlisberger has rewarded them with a once-in-a-generation rookie season, winning his first eight starts despite sometimes shaky stretches of indecision during Sunday’s 19-14 victory in Cincinnati.

On defense, Pro Bowl nose tackle Casey Hampton’s season-ending knee injury in Week 6 seemed huge because he is the Steelers’ primary run-stopper. But backup Chris Hoke has been an excellent replacement, considering he never played during his first three NFL seasons.

“One thing about this team is we’re an unselfish team,” said wide receiver Plaxico Burress, who will miss Sunday’s game against Washington (3-7) because of a sore hamstring. “It’s not about one person on this team, we’re not trying to feature one guy.”

Some other inexperienced players have helped, too. James Harrison, who had practiced only on special teams, had four tackles and a sack when linebacker Joey Porter was ejected for fighting before the Nov. 14 game in Cleveland.

The offseason signing of 13-year cornerback Willie Williams also attracted little attention. He didn’t start for Seattle in 2002 or 2003, and the Steelers had two young cornerbacks — 2004 second-rounder Richard Colclough and 2003 fourth-rounder Ike Taylor — ready if either Chad Scott or Deshea Townsend got hurt.

But when Scott (quadriceps) was injured Oct. 17 in Dallas, Williams took his place and has kept the job, though Scott could return soon.