Technically, you could blame the defense for the 49ers’ 20-17 loss to the Seahawks on Sunday because the defense couldn’t close out the game. It gave up an 80-yard touchdown drive to Geno Smith in the final moments. That’s not good.

But the defense played well overall, giving up only 20 points. Meanwhile, the offense scored just 17 points. That’s well below the 49ers’ standards.

Just a month ago, the 49ers played the Seahawks in Seattle and scored 36 points. Granted, the Seahawks were missing a few key starters on defense and have since added three new starting linebackers, so they have improved. Yet Kyle Shanahan is primarily responsible for the 49ers’ uninspiring offensive production.

In Seattle, the 49ers rushed for 233 yards. And that’s because Jordan Mason and Isaac Guerendo were excellent. Mason averaged 8.1 yards per carry and Guerendo averaged 9.9. And together they ran the ball 19 times.

On Sunday at Santa Clara, Christian McCaffrey rushed the ball 19 times and averaged just 4.2 yards per carry. He wasn’t 100 percent himself. Meanwhile, Mason carried the ball twice for 13 yards (6.5 yards per carry) and Guerendo never touched the ball.

If Shanahan had simply played the running backs who did so well against the Seahawks four weeks ago, the 49ers likely would have won. The Seahawks in particular just can’t stop Mason. We saw that this Sunday in his two carriers.

Shanahan has accomplished a lot in the NFL, but his inability to consistently play against his best players is troubling. It wasn’t until this year that he found out that Jauan Jennings is a Pro Bowl-caliber wide receiver.

If the 49ers want to turn their season around, they need to play their best players.

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