The San Francisco 49ers' stellar defense is a major reason they enter the second half of the season in control of the NFC West, at times overshadowing an offense possessing an efficient quarterback and the NFL's best running game.

Alex Smith, Frank Gore and the rest of the 49ers' offense look to take advantage of a St. Louis Rams team that hasn't forced a single turnover during a three-game losing streak when the division rivals meet Sunday in San Francisco.

Defense has been a staple of coach Jim Harbaugh's squad that is allowing an NFL-low 12.9 points per game while giving up an NFC-best average of 271.4 total yards.

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San Francisco (6-2) has won four of five, allowing a total of 12 points without a single touchdown in the victories after beating Arizona 24-3 on Oct. 29 before its bye week.

The offense hasn't been bad, either. Smith ranks fourth in the league with a 102.1 passer rating after finishing 18 for 19 for 232 yards and three touchdowns - two to Michael Crabtree and another to Randy Moss - versus the Cardinals.

Gore had only 55 yards on 16 carries, but he's a big reason the 49ers lead the NFL with 168.6 yards per game on the ground. Three victories during San Francisco's hot stretch have come by at least 21 points.

"When you see other teams, other players, you see one or two guys having big stats," Gore said. "In this offense, it's different. There's so much talent around here."

Though Harbaugh surely is pleased with his team's effort on both sides of the ball, he knows there's plenty of work to be done if the 49ers hope to play in their first Super Bowl since the 1994 season.

"A simple approach to how we understand success is to get better today than we were yesterday. Be better tomorrow than we were today," Harbaugh said. "Feel like improvement will lead to wins. And wins will lead to championships. It's an improvement-equals-success theory."

San Francisco has committed only nine turnovers, and the chances of that number increasing against struggling St. Louis seem slim.

The Rams (3-5) took an early 7-0 lead before allowing 45 unanswered points in losing to New England on Oct. 28 in London before their bye week.

It also marked their third consecutive game without a takeaway. They've forced only two fumbles all year, much to the dismay of coach Jeff Fisher.

"It's highly unusual that in eight games and all the touches that are involved in eight games, our opponent has fumbled two balls and we've recovered one," Fisher said. "We need to place a great deal of emphasis on that and getting the ball back."

The Rams, who only have nine total takeaways, haven't gone four straight without forcing a turnover since at least 1950.

"We have got to find a way to come up with some big plays," linebacker James Laurinaitis said. "Defensively, we have got to force some turnovers. We are in a drought with that right now, so how do we force some turnovers? How do we make some plays? How do we score on defense? How do we impact the game more?"

On offense, Sam Bradford has been solid during the team's skid, completing 67.0 percent of his passes, including a 50-yard touchdown to Chris Givens against the Patriots.

Bradford missed both meetings with the 49ers last season while recovering from a high left ankle sprain, but he has a 73.4 completion percentage and 100.3 rating with two touchdowns in two career starts versus San Francisco.

"He's always been a pretty top-notch guy (and has) all the things you look for from a top notch quarterback in this league," Harbaugh said. "He's got a calm demeanor in the pocket. Excellent technique, footwork, arm strength, real good location."

Bradford could benefit from the return of favorite target Danny Amendola, who still leads St. Louis with 32 catches and 395 yards despite missing the last three games with a collarbone injury.

"It's feeling good right now, I have full range of motion and strength and everything," Amendola said.

Smith threw for 213 yards and Crabtree caught two touchdowns - one on a fake field goal - in the 49ers' 34-27 victory in the most recent meeting Jan. 1, marking their seventh win in the last eight matchups.

St. Louis hasn't won in San Francisco since 2007, dropping four straight and six of the last seven there.