Defense Sustains 49ers in Playoff Win Over Saints SAN FRANCISCO - The hit that changed momentum, that left New Orleans running back Pierre Thomas crumpled on the field, that made the Saints think twice when they ventured across the middle, came early into the first quarter Saturday afternoon. It came from Donte Whitner, the safety who spied Thomas in the right flat and closed the gap between them. He bludgeoned Thomas with such force that their collision echoed across the stands, helmet meeting helmet, smack, then crack. With that hit, Whitner had delivered the intended message from the 49ers" defense, which lined up against an offense as productive as any in N.F.L. history and a quarterback who set three single-season passing records, and essentially punched both square in the face. The 49ers controlled this game on defense, often through sheer, physical force. Later, the 49er defense would need help from the offense. The defense would yield two long touchdowns, and the offense, against all odds and common sense, matched the Saints" scoring late in the fourth quarter. But it was the defense that made the 49ers" 36-32 victory possible. If this was, if this is, the year that offense ruled the N.F.L., the 49ers are an exception, an anomaly, the team that wins games its offense does not lose. San Francisco, the team that unleashed the West Coast Offense on professional football, that lifted the pass to historic levels, advanced to the N.F.C. championship game next week with an offense that stalled and plodded and a defense that swarmed and plowed. The 49ers played defense the way the Pittsburgh Steelers played defense in recent seasons, the way the Chicago Bears played defense in the 1980s. They dominated the Saints at the line of scrimmage, hit them often, hit them hard. They made quarterback Drew Brees, at once a candidate for league M.V.P. and perhaps the greatest season ever for a quarterback, look as ordinary as their own signal caller, the steady game manager, Alex Smith. In the Saints" playoff victory last weekend against Detroit, Brees and the offense gained an N.F.L. postseason record 626 yards, as if operating in fast forward. Late in the first quarter, though, the 49ers defense took over, ahead, 7-0, as if unaware the Saints had scored 45 points in each of their previous three games and 42 in the game before that. Brees looked deep down field to receiver Adrian Arrington on a post route, same as so many times throughout this season, and Arrington appeared to have a step on the defender guarding him. Instead, safety Dashon Goldson read the pass, stepped in front Arrington and rumbled 41 yards after securing the interception. Two plays later, Smith found receiver Michael Crabtree on a slant route for a 4-yard score. After New Orleans fumbled the ensuing kickoff, after David Akers booted a 25-yard field goal and the 49ers led, 17-0. Their defense was their offense. There would ultimately be glitches, such as late in the fourth quarter when Brees hit running back Darren Sproles for a short pass that Sproles turned into a 44-yard gain that ended in the end zone. The Saints led, 24-23, but not for long, not after the 49ers offense marched down field and scored again. Such late-game heroics would not have been possible without the 49ers" defense, which delivered its message with force on Saturday and held on late against the Saints. There went Brees, with two minutes remaining, the ball in his hands again. There went the Saints, with another touchdown, this time from Jimmy Graham. The Saints did finish with 32 points on Saturday. But this was both below their recent average, and on this day, not enough.