And both of their scores were helped by special teams - a long punt return by Jim Leonhard and a poor punt by the Steelers - and set up by pass-interference penalties.
Still, the defense refused to point fingers at either the offense or Flacco, who has been roughed up by the Steelers in three losses to Pittsburgh this season.
"I didn't think he struggled," linebacker Terrell Suggs said. "They just made plays. It was their night. He was getting hit when he was throwing. He made the AFC championship in his first year. The only thing is up for him."
Flacco, though, never could get in a rhythm because of the Steelers' relentless pass rush and his inaccurate passing.
When Holmes' long touchdown put the Ravens into a 13-0 hole, Flacco had misfired on seven of his first eight passes.
At that point, the Ravens hadn't gained a first down and were out-gained 156-17.
The Ravens' offense got a break near the end of the second half with special teams and a questionable call by the officials.
Leonhard's 45-yard punt return set up the Ravens at the Steelers' 17-yard line. On third-and-nine, Steelers cornerback Bryant McFadden appeared to break up a pass to Mason cleanly, but the officials flagged him for pass interference.
Then McGahee scored on a 3-yard run - his first postseason touchdown - to cut the deficit to 13-7.
The Ravens inched closer in the fourth quarter when Pittsburgh's Mitch Berger shanked a 21-yard punt. A second pass-interference penalty by the Steelers - this time by cornerback Ike Taylor on rookie wide receiver Marcus Smith in the end zone - set up another Ravens score.
McGahee ran in from 1 yard out to close the score to 16-14 with 9:29 left in the game.
But turnovers on their last three possessions (two interceptions by Flacco and a fumble by McGahee) ended any hopes of a comeback.
Suggs said the loss has yet to set in with the players.
"We're still feeling a little shocked and disappointed," he said.
After the Ravens fell short of reaching the Super Bowl, Harbaugh remained upbeat in his final message to the team.
"This is our beginning. This is where we start," he said. "This is not an end by any stretch. We're excited to go forward and take the next step."