"If there was a team that you could put up as a poster boy for a 53-man roster, it's us," said St. Pierre, the Steelers' third-string quarterback, who was activated off the practice squad Friday. "It's special."
And so are the Steelers, who didn't need Ben Roethlisberger, Jerome Bettis or a host of other starters to win their 14th straight to match the single-season record set by Miami in 1972. The Steelers also became just the fourth team in NFL history -- and first in the AFC -- to finish 15-1.
Parker, an undrafted rookie free agent, had 102 yards rushing, including a 58-yarder that set up Jeff Reed's 37-year field goal, Pittsburgh's go-ahead score.
And then there was Harrison, the backup linebacker, who returned a fumble 18 yards for a touchdown to seal the victory.
"It says a lot about the backups and the character of this team," Harrison said. "It's a sense of pride. You don't want to lose to anybody."
The Steelers, who had clinched home-field advantage in the AFC playoffs, knocked off a Bills team that was among the hottest in the league. Buffalo had a chance to earn its first playoff berth since 1999.
"Pretty angry. ... I'm a little bit in shock," said red-eyed quarterback, Drew Bledsoe. "The bottom line is if we can't beat them with their backups on the field, then we probably don't deserve to be in."
The Bills (9-7), who had overcome an 0-4 start, had a six-game win streak snapped. Their loss automatically put the New York Jets in.
"It's rough," left tackle Jonas Jennings said. "Everything was set up for us and ... we had to come out and handle our business and we came up short."
Buffalo made it close when Willis McGahee scored his second touchdown of the game on a 1-yard plunge with 78 seconds left. But the Bills failed on an onside kick when Steelers cornerback Ike Taylor smothered the ball.
The Bills looked nothing like a team that outscored its opponents 228-89 in its previous six games.
Buffalo managed just 267 yards, with seven three-and-outs. And the defense couldn't get the Steelers off the field, losing the time-of-possession battle by more than 11 minutes.
The game turned late in the third quarter after Buffalo's Rian Lindell missed wide right on a 28-yard field goal that left the Bills clinging to a 17-16 lead.
The Steelers responded with 10 points in an 85-second span at the start of the fourth quarter.
Following Reed's field goal, Bledsoe was blind-sided by rookie cornerback Ricardo Colclough, who forced a fumble that fell directly into Harrison's hands.
The Bills went three-and-out on their next possession and the Steelers then ate up nearly nine minutes with a 14-play, 46-yard drive helped by two defensive penalties. It was capped with a 33-yard field goal by Reed, who kicked five.
St. Pierre extended the drive with a 2-yard bootleg on fourth-and-1 at the Bills 37.
Antwaan Randle El also scored on a 16-yard Maddox pass.
"15 and 1, baby!" Steelers running back Duce Staley yelled as he headed to the locker room.
Roethlisberger was bubbling following the performance.
"I told someone, `If I'm dreaming, I don't want to wake up because I want to keep this going,"' Roethlisberger said. "What's so special about this team is everyone is selfless."
The Steelers have two weeks to await their next opponent. The Bills have a long offseason to ponder what went wrong.
"It's frustrating because I want more for this organization, especially the fans," said receiver Eric Moulds. "I feel like they deserve more than what we showed today."
Bills' owner Ralph Wilson remained upbeat.
"We had a bad day and it didn't work out," Wilson said. "I'm really looking forward to next year, because we have something to build on."
- McGahee had 79 yards rushing and two scores. Bills CB Nate Clements also scored on a 30-yard interception return.
- Parker became the third Steelers player to rush for 100 yards this season.
- Bledsoe finished 16-of-30 for 189 yards. The former Patriots star has 10,151 yards passing in three seasons with Buffalo, becoming only the seventh NFL player to surpass 10,000 yards with two teams.
- The Steelers also rested WR Plaxico Burress and CB Deshea Townsend.