SEATTLE – Defensive lineman Ricky Jean Francois said last week he expected the Seahawks might run straight at him in his first game substituting for ironman Justin Smith.

They obliged.

On their second offensive play, Seattle called a run to the right side of the 49ers' defense. Marshawn Lynch got past Jean Francois at the line of scrimmage, then found little resistance from San Francisco's other 10 defenders.

Lynch finished with 111 rushing yards, the third straight time he has passed the 100-yard mark against the 49ers, who continued a slide that began last week in the second half against New England. They allowed 176 rushing yards against Seattle, a season high.

It was no coincidence that for the first time in five seasons, the 49ers played a full game without the anchor of their defense. Carlos Rogers called Smith "one of the MVP's" of the defense.

"He demands a double team, he'll get after the quarterback," Rogers said.

"When (opponents) scout our defense and talk about our D-line, they're going to scout Justin. He makes it easier for our linebackers. He makes it easier for Aldon (Smith) to get sacks. He's a big part of our defense.

"But the thing about it is, the next guy's going to step up. We can't use Justin being out as an excuse."

Smith was declared inactive before the game, ending his consecutive starts streak at 185. He injured his elbow in the third quarter of last week's game. He tried to return to that game but could not, and he missed the week of practice before Sunday's contest.

Now his availability for this week's regular-season finale against the Arizona Cardinals – and indeed the playoffs – is up in the air. Asked whether Smith would be back for the postseason, coach Jim Harbaugh said, "I don't know for sure."

Jean Francois, meanwhile, finished with six tackles to lead all of the 49ers' defensive linemen. He said he adjusted after the early attack by the Seahawks "but there were still a few breakdowns here and there."

"The majority of their shotgun reads or stretch (runs) were going to come at me," Jean Francois said. "It just slowed down after a minute. Then it started back up. It didn't matter what the score was, I had to keep playing."

Without Smith, the 49ers activated nose tackle Ian Williams for the first time this season, and the second-year player ended up playing about a dozen snaps. Another defensive lineman, Will Tukuafu, suffered a back injury in the third quarter and did not return.

Smith had the NFL's third-longest starting streak among active players and the longest for a defensive lineman.

Aldon Smith trails – Houston defensive lineman J.J. Watt had a sack Sunday, giving him 20 1/2 on the season and allowing him to pull one sack ahead of 49ers defensive end Aldon Smith, who was held without a sack for the second straight game.

Smith and the 49ers wrap up the season against the Cardinals, who have allowed a league-high 56 sacks this season. The Texans play the Indianapolis Colts, who have surrendered the 10th-most sacks.

Et cetera – With Vernon Davis (concussion) out of the game, undrafted rookie Garrett Celek filled in at tight end and finished with two catches for 41 yards. Delanie Walker, meanwhile, had four catches for 54 yards, including an 18-yard touchdown, his second straight game with a score.

• Rookie outside linebacker Cam Johnson, who was promoted from the practice squad Saturday, suited up against the Seahawks. Johnson, a seventh-round pick out of Virginia, was tapped to replace Clark Haggans, who was out because of a shoulder injury. The only active player who didn't set foot in the game was Alex Smith.

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