49ers defense looks to build off great game against Eagles and regain its old dominant form

San Francisco's once-dominant defense is beginning to rediscover the swagger that has defined this unit in recent years.

Second-year safety Eric Reid and several of his defensive teammates were thrilled with the way they kept Philadelphia quarterback Nick Foles from beating them last week. The Eagles didn't even get past midfield until the closing minutes of the 26-21 victory by the 49ers, and San Francisco did it without a single penalty on the defensive side.

The 49ers (2-2) realize if they are unable repeat such an effort against Alex Smith and the Chiefs (2-2) this Sunday, last week will all be for naught.

"This one doesn't mean anything if we don't get another win next week," Reid said. "It was huge. We needed a win, we needed it to kickstart our season."

San Francisco had given up costly plays in the passing game while losing to Chicago in Week 2, then experienced problems stopping the run in a defeat at Arizona the following week.

The 49ers defense held the Eagles to 213 total yards, including just 22 rushing, for the lowest total under Philadelphia coach Chip Kelly.

San Francisco features the NFC's top run defense with 69.8 yards allowed, and second-best in the NFL behind the Jets (63.3). The Niners have surrendered only 152 yards rushing in their past three games, fewest by the team over a three-game stretch since 1997.

On Sunday, the Chiefs present another challenge altogether with a talented, two-headed running back tandem in All-Pro Jamaal Charles and the guy who has emerged as a perfect complement, Knile Davis. Charles scored three touchdowns in Monday night's rout of the Patriots, two of those TD receptions.

"It's a very complex offense, they do a lot of different things," defensive coordinator Vic Fangio said Thursday. "Alex is a very athletic and fast quarterback that sometimes people forget about but it stands out when you watch the tape. The offense is operating at a high level for them coming off that game."

San Francisco has plenty of familiarity with the man under center — 2005 No. 1 overall draft pick Smith, traded by the 49ers to the Chiefs in March 2013.

Asked Thursday about getting any tips from coach Jim Harbaugh about defending Smith, Fangio said that's unnecessary.

"I was here, too, for that time period," he said of the tail end of Smith's tenure. "Sometimes too much study is paralysis by over-analysis. I watched the tape and prepared for him like any other quarterback. I saw him play a lot of those games and in practice."

Fangio's new-look secondary has come into its own.

Perrish Cox has proved a reliable replacement for injured starting cornerback Tramaine Brock.

"We always come in with a lot of confidence," Cox said. "I think these past two weeks, those games we were up going into the half. We just didn't finish. All week long, we wanted to finish. Just keep pounding. Like I said, as a team, we did it together."

When Brock does return from a toe injury, it's unclear who will start.

"We'll figure that out then," Fangio said.

Safety Antoine Bethea earned NFC Defensive Player of the Week after making his first interception since joining the 49ers to go with a forced fumble and seven tackles.

"Words can't describe some of the plays he made out there," linebacker Patrick Willis said. "He was all over the place."

Reid and Bethea have found a rhythm, while offering as much help to rookie nickel back Jimmie Ward as possible.

Reid, for one, isn't as familiar with Smith this week given that the quarterback was already gone when the 49ers selected Reid with their top draft choice last year.

"It might be a little strange for some guys who were close with him, but he's an opponent now so we've got to beat him," Reid said.

NOTES: Asked about rookie Aaron Lynch's swift improvement, Fangio cracked, "Good coaching." ... TE Vernon Davis (back spasms) and RT Anthony Davis (knee), both hurt against the Eagles, weren't practicing when the afternoon workout began.

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