Until Sunday, Vic Fangio's defense had been a 49ers' strength, with five quarterback sacks, six quarterback hits and 13 hurries to its credit.
But as the 49ers headed to the locker room after a stunning 24-13 loss to the Minnesota Vikings, Fangio's unit had to be severely disappointed with its performance.
As a team, the 49ers' defense never played up to potential in Minneapolis. The Vikings rolled up 344 yards of total offense, converted 7-of-14 third-down attempts and possessed the ball for 33:28, an impressive number considering neither the Packers nor Lions broke the 30-minute mark against the 49ers earlier this season.
Yet the most frustrating aspect of the defense's play was its inability to pressure Vikings QB Christian Ponder, who was only hit twice. There were no sacks in the box score. The pressure was scarce at best. And when it did get close to the Vikings QB, Ponder would just find a crease in the defense and take off running.
His legs proved to be his most valuable asset, helping him put together three touchdown drives that spanned 10-plus plays and 80 yards each time. Doing that once against the 49ers' vaunted defense is impressive, but three times is almost unheard of.
The only thing San Francisco's defense did well was stop the run. Going into this game, the general consensus was that if you stopped the run, the rest would take care of itself. I'm not sure anyone predicted that Vikings' quick passing game would be so effective against what had been the most dominant defense in the NFL.
To make matters worse, 49ers QB Alex Smith decided to have his worst game since last Thanksgiving. His two late-game turnovers were his first since Week 12 of the 2011 season.
Trailing 17-3 at halftime, the 49ers were never able to establish the run. Frank Gore did well with his limited touches, averaging 5.3 yards per carry, but a 38/20 pass-to-run ratio is not the style of game Jim Harbaugh likes to call.
Offensively, 280 yards isn't going to cut it. The last time the 49ers' yardage total was that low was in Week 14 last season in a 21-19 loss to the Arizona Cardinals. Coincidentally, that was also the last time the offense rushed for fewer than 90 yards.
This team is built on the run game, so trying to overcome a 14-point deficit through the air is a challenge for the 49ers. In fairness to San Francisco, it's not always a challenge, but when teams can tee off on Smith, it's doubtful the 49ers will make many successful comeback runs.