The team the 49ers will face Sunday isn't the same team they handled with ease in Week 4.
The Rams were the league's worst rushing team then, as they demonstrated by rushing 19 times for 18 yards in a 35-11 home loss to the 49ers.
Since then, the Rams have run back to relevancy, both on the field and in the standings. With a rushing attack that now ranks 15th in the league, the Rams (5-6) have won their last two games, routing the Indianapolis Colts and the Chicago Bears by a combined score of 80-29.
"They're just a lot better, and they're playing like it," 49ers defensive tackle Justin Smith said.
Keying that surge are rookie rushers Zac Stacy and Benny Cunningham. Neither saw much action in the September loss to the 49ers, with Stacy getting no carries and Cunningham totaling four carries for 6 yards and a 17-yard reception.
"They've found their two backs now that they're comfortable with," 49ers defensive coordinator Vic Fangio said. "And they're just blocking and running very good right now."
Stacy missed practice time this week before getting cleared Friday after passing post-concussion protocol. He has four rushing touchdowns in the past three games, and he's run for 620 yards since entering the starting lineup the week after the 49ers game.
Still, the 49ers won by 24 last meeting -- on the road, on three days' rest. Smith, however, indicated the final score didn't indicate how closely matched these teams are.
Last season's scores did, however: a 24-24 tie last November and a 16-13 Rams victory in overtime three weeks later.
"They're playing very physically," 49ers coach Jim Harbaugh said. "Their running back is playing very well. They are rushing for yards. They've put up some real good numbers rushing the football. It's made them a very balanced team."
Harbaugh went so far as to say Kellen Clemens has done a "marvelous job" of replacing injured quarterback Sam Bradford. Clemens will be making his fifth start, and the 49ers are expecting him to use play-action fakes to create shots downfield to the Rams' young wideouts.
One such threat is rookie Tavon Austin, whose play-making skills earned him NFC Special Teams Player of the Month honors for November. In the past two wins over Indianapolis and Chicago, he produced a 98-yard punt return, touchdown catches of 57 and 81 yards, and a 65-yard rushing touchdown.
Austin, drafted No. 8 overall in April, didn't fare well in his first game against the 49ers, averaging 3.2 yards on six punt returns, including one he muffed. Of the eight passes targeted for him, he caught two for 6 yards.
Recalling a predraft visit to the 49ers, Austin said on a conference call last week: "I definitely thought they could have used me over there."
The 49ers' defense prides itself on not allowing big plays. But stopping the run is their main objective. Combine those two priorities and you get this: only two runs allowed over 20 yards all season, a 30-yarder by the Jacksonville Jaguars' Maurice Jones-Drew and a 27-yard touchdown run by the Carolina Panthers' DeAngelo Williams.
That run defense might be not be ranked in its normal stratosphere -- No. 12, at 104.7 yards per game -- but it's typically stout at home. Since 2009, the 49ers are allowing 96.4 rushing yards at Candlestick Park, the fourth-best average in the league.
The 49ers defensive front likely will be without Ray McDonald for a third straight game because of a left-ankle sprain.
Offensively, left guard Mike Iupati will miss a second straight game with a sprained left knee. But the 49ers do expect standout wide receiver Michael Crabtree to make his season debut.
"I guess it's time for me to go," said Crabtree, who tore his right Achilles on May 21. "I feel comfortable enough to go out there and play, to go out there and see what I can do."