Not only is the unit giving up the ninth-fewest yards per game in the league, but they are allowing just 13 points per game, the fewest in the NFL.

For years, the offense served as the team’s main attraction. But the Colts’ defense continues to improve and prove to critics they are equal to their offensive counterparts.

“If people believe it, great. If they don’t, that’s alright,” defensive end Dwight Freeney said. “We’re going to keep moving, doing what we do week-in and week-out and just keep the ball rolling and have fun out there.”

On Sunday against San Francisco, the defense surrendered 295 total yards and forced the 49ers to punt eight times, six of which came on three-and-outs.

“Our defense rose to the occasion when we needed it most,” Colts Head Coach Jim Caldwell said after his team’s 18-14 victory over the 49ers on Sunday. “We needed a couple of big stops to knock them out of field-goal range and that was huge. We were pleased with their effort.”

The defense saved one of its best performances for the second half Sunday, when they forced San Francisco to punt on three of their four possessions. The 49ers’ other second-half drive resulted in a fumble, which was forced and recovered by rookie defensive back Jerraud Powers.

“There were like three of us that hit (San Francisco rookie wide receiver) Michael Crabtree,” Powers said. “I rolled over and started to get up and felt the ball, and I heard (rookie defensive back Jacob) Lacey saying, ‘Go, go, go, go.’ So I picked it up and tried to get whatever I could. It was a big play.”

The fumble was one of several big plays for the Colts defense. In his second game back, safety Bob Sanders intercepted a pass in the first quarter. The Colts’ pass rush put pressure on San Francisco quarterback Alex Smith all game and produced four sacks.

Powers said the defense is playing well, but does not believe the unit has reached its potential yet.

“We’re in the middle course of the season and we’re trying to climb and get better each week,” he said. “We played decent (Sunday), but we also had a few errors. We have room to make improvements, and that’s always a plus coming off a victory when you played well.”

One of the Colts’ four sacks Sunday came at the hands of Freeney, who extended his streak of consecutive games with a sack to eight.

In addition to Freeney, defensive tackle Antonio Johnson, defensive end Robert Mathis and linebacker Philip Wheeler registered sacks.

“That’s the mentality around here,” Freeney said Sunday. “Defensive line, linebackers, safeties, corners, the defense in general. We want to be out there making plays when it counts. Put everything on our shoulders, that’s our mentality.”

With the Colts scoring 42 points at St. Louis, linebacker Gary Brackett said Sunday was the defense’s turn to step up.

“That’s why it’s a team. There’s three phases. Each week it might be our turn to step up,” he said. “This week it was our job to hold them to 14 points.”

The Colts also held San Francisco running back Frank Gore in-check when they needed to most.

The Pro Bowl back ran for 73 yards in the first half, including a 64-yard touchdown up the gut in the first quarter.

But Indianapolis improved in the second, holding the 2006 NFC rushing champion to just 18 yards rushing after halftime.

“To slow a back down as good as he is, I think we are moving in the right direction. I think we are coming along,” Caldwell said on Monday. “We are doing some good things.”

The Colts coach said every week has been “a real test” for his team, and he sees his squad getting better every week.

Against the 49ers, the defense turned in one of its best performances of the season.

“We may not have been perfect, but we found a way to win,” Caldwell said.