Justin Smith’s health key for 49ers

San Francisco and Atlanta both passed significant milestones last Sunday.

The 49ers won a divisional game with Colin Kaepernick at quarterback, getting just as far as the benched Alex Smith got them last season. So now we’ll see whether the second-year Kaepernick can take the club the next step, getting it to its sixth Super Bowl.

The Falcons, who had been 0-3 in postseason games under Coach Mike Smith, finally picked up their first playoff victory under his tutelage, and now have a chance to prove wrong all their doubters.

Key for the 49ers is health of Pro Bowl defensive lineman Justin Smith, who played most of the defensive snaps last week despite a brace-protected partially torn triceps.

Smith frequently commands double-teams, which frees Aldon Smith, who has 19 1/2 sacks but has not collected one since Justin Smith was injured in Week 15.

In his return last Sunday, Justin Smith had four tackles and an assist against Green Bay. He said his injured arm is in relatively good shape for the Falcons game.

“It’s doing its job, and it felt pretty strong,” Smith said this week. “Doing anything the second time is better than the first time, so it should definitely be a lot better, a lot more comfortable.”

Soaring

Atlanta started the season 8-0 for the first time in franchise history and finished with a 13-3 record, earning the NFC’s No. 1 seeding.

The Falcons became the ninth team since realignment in 2002 to start a season 8-0. With a victory Sunday over San Francisco, they would become the fifth such team to reach the Super Bowl. Two of the four teams to accomplish the feat went on to win the Super Bowl (2006 Indianapolis and 2009 New Orleans). Teams to begin a season 8-0 or better since realignment in 2002:

Double play

San Francisco Coach Jim Harbaugh has compiled a 26-8-1 (.757) record in his first two seasons (including the postseason), and led his 49ers to two NFC West titles and a second consecutive NFC championship game.

Harbaugh became the fifth head coach since 1970 to reach the conference championship game in each of his first two seasons, joining Don McCafferty, Rex Ryan, George Seifert and Barry Switzer.

With a win Sunday, Harbaugh (26) can tie Steve Mariucci (27) for the third-most victories by a head coach in his first two seasons in NFL history, including the playoffs. Head coaches to reach the conference championship in each of their first two seasons since 1970 (*won Super Bowl):

Another view

ESPN’s Trent Dilfer: “Sometimes the most powerful thing in football is confidence, which you can’t quantify. It’s momentum that you can’t quantify. It’s will, competitive will, to make big plays in big moments. There’s no number to support. When I look at the Falcons in that light, I see a lot of that stuff.”

By the numbers

How teams compare statistically during the regular season. All stats are per-game averages, except for sacks and turnover differential, which are for the season (league rank in parentheses):

Farmer’s pick

The Falcons have had problems stopping running quarterbacks this season, so Kaepernick figures to present big problems. San Francisco’s offense ground to a halt in the championship game last season. That won’t happen Sunday. On defense, the 49ers will contain Atlanta’s run better than Seattle did, even with Justin Smith not at 100%. 49ERS 31, FALCONS 24.