When the 49ers (14-4) have the ball:
San Francisco runs the ball as well as anyone left in the playoffs, with RB Frank Gore (21) as the focal point, but QB Colin Kaepernick (7) as the wild card. The 49ers will try to establish something on the ground immediately behind a strong line led by left tackle Joe Staley (74) and guard Mike Iupati (77). That means plenty of Gore inside and even a bit outside, and Kaepernick using his speed - unmatched by any quarterback in the league - to get to the edge.
But Gore has struggled at Seattle, and the Seahawks command the line of scrimmage as well as any team, even San Francisco. They ranked seventh at stopping the run, with huge tackle Brandon Mebane (92) clogging the running lanes. Seattle's other D-linemen, particularly Red Bryant (79) and Michael Bennett (72), are versatile and rugged.
If the 49ers can't get the rushing game going, it lets Seahawks linebackers Bobby Wagner (54) and Bruce Irvin (51) get even more involved. It also means Bennett, DEs Chris Clemons (91) Cliff Avril (56) and Irvin will be more of a threat in the passing attack, although trapping and sacking Kaepernick is no easy chore.
Kaepernick struggled mightily in the Niners' 29-3 loss at Seattle in September and has performed poorly at CenturyLink Field in both of his appearances. He's a more mature player now and is 3-0 in road playoff games.
To get to 4-0 might require more use of his arm than coach Jim Harbaugh prefers. And that's where the most intriguing matchups of this game will occur: San Francisco's receivers against Seattle's secondary.
WR Anquan Boldin (81) helped Baltimore beat the 49ers in last year's Super Bowl, and he has had a superb season. Since WR Michael Crabtree (15) returned from a torn Achilles tendon, the 49ers haven't lost, including a win over Seattle, and their air game has risen to another level. Throw in Vernon Davis (85), the best deep threat in the league among tight ends, and the Seahawks' terrific group of DBs will be heavily challenged.
All-Pros CB Richard Sherman (25) and S Earl Thomas (29) are elite in coverage and will make for a juicy encounter with San Francisco's receivers. Sherman led the league with eight interceptions, Thomas had five. The other starting safety, Kam Chancellor (31), is almost as good, especially standing out in run defense, and CB Byron Maxwell (41) has been a real find since Brandon Browner (39) was suspended by the NFL.
When the Seahawks (14-3) have the ball:
Seattle's offense has slumped in recent weeks, but it also has made big plays when needed. RB Marshawn Lynch (24) is Gore's counterpart and comes off a great game vs. New Orleans: 140 yards and two touchdowns. He's a similar-type runner and when in "Beast Mode," he's as tough as they come.
Then again, so is San Francisco's run defense, led by do-everything tackle/end Justin Smith (94) and linebackers NaVorro Bowman, an All-Pro, Patrick Willis and Ahmad Brooks. The Niners aren't quite as deep up front as Seattle, but they make up for it with the NFL's top linebacking corps.
Coach Pete Carroll is most comfortable when Lynch is on the loose, which makes things much easier for QB Russell Wilson (3). If the 49ers can control Lynch, who averaged 105 yards rushing at home against them, it puts a heavy onus on Wilson, whose passing numbers have been pedestrian recently.
Wilson, of course, is like Kaepernick with his escapability. While not as fast as Kaepernick, Wilson is more elusive and keeps passing plays alive with his uncanny scrambling. That's something 49ers DBs Tramaine Brock (26), Eric Reid (35), Donte Whitner (31) and, if he's recovered from a hamstring problem, Carlos Rogers (22) must be aware of at all times.
Like San Francisco, Seattle prides itself on an unrelenting physical offensive line. It's anchored by center Max Unger (60) and tackle Russell Okung (76), but it's also deep because injuries forced backups into action all season.
They'll face a hefty challenge trying to keep LB Aldon Smith (99), Justin Smith and San Francisco's other prime sackmasters away from Wilson. Then again, those defenders might get tired chasing Wilson.
Where the Seahawks don't equal the 49ers on offense is at receiver. There's not a lot of star power there, especially if Percy Harvin (11) can't go because of concussion symptoms.
Still, don't underestimate the hands of Doug Baldwin (89), the moves and quickness of Golden Tate (81) or the steadiness of TE Zach Miller (86).
No real big edges here unless Harvin is healthy - he's a gamebreaker on returns.
Tate probably is the next-best weapon on either side running back kicks.
Both sides treasure the reliability of their kickers. San Francisco brought in veteran PK Phil Dawson (9) as a free agent after David Akers flopped last season. Dawson has excelled, and he beat Green Bay in the wild-card round with a final-second field goal through the frigid night air. Punter Andy Lee (4) has been a perennial Pro Bowler.
Seattle counters with PK Steven Hauschka (4), who also has had a topnotch season, and Jon Ryan (9), who regularly buries punts deep in opponent's territory.
Harbaugh and Carroll have no love lost, dating to when they were at Stanford and Southern Cal and Harbaugh ran up the score, prompting Carroll to ask him, "What's your deal?"
Harbaugh's deal has been winning like no coach in San Francisco since Bill Walsh. This is the Niners' third straight trip to the NFC title game under him. He exudes confidence and, yes, arrogance, and it works for the 49ers.
Carroll's nonstop exuberance rubs off on his players, and no team is more aggressive, especially on defense, which is Carroll's specialty. He had some success in a previous head coaching stint with the Patriots, then went to USC and, since returning to the pros, Carroll has done a brilliant job turning the Seahawks into a championship contender.
Playing in the same division means both sides are deeply familiar with each other; there won't be many secrets on display here.
That the Niners have struggled in the Pacific Northwest is, well, tangible: They were outscored 71-16 in their last two visits, Harbaugh's two worst losses. They're an experienced outfit in pressure situations, though, so the supersonic noise from the 12th Man in the stands shouldn't affect them.
But it has. And it figures to be louder than ever on Sunday.