Rapid Reaction: 49ers 25, Lions 19

DETROIT -- A few thoughts on the Detroit Lions' first loss of the season:

What it means: The Lions lost for the first time since Week 12 of the 2010 season, missing an opportunity to start 6-0 for the first time since 1956. The end came dramatically in a seesaw game: The San Francisco 49ers' Delanie Walker scored on a 6-yard pass on fourth down with 1 minute, 56 seconds remaining. Officials reviewed the play to determine whether Walker's right knee hit the ground before the ball crossed the plane. I saw no angle to suggest that it did.

MegatronWatch: It's time to launch an investigation. Lions receiver Calvin Johnson didn't catch a touchdown pass for the first time all season. He did, however, haul in six passes for 102 yards, including a 41-yarder that set up a go-ahead, fourth-quarter touchdown.

"Process" call redux? Surely you remember the touchdown that Johnson lost against the Chicago Bears in Week 1 of the 2010 season. I honestly thought the Lions would fall victim to the same "process of the catch" rule Sunday when receiver Nate Burleson caught what appeared to be a 5-yard touchdown pass early in the fourth quarter. Burleson got both feet in bounds, but he used the ball to brace himself as he stepped onto the netting behind in the end zone. The ball remained on the ground, and referee Mike Carey ruled the pass incomplete. Carey reversed the call after a challenge from Lions coach Jim Schwartz. As much as I hate the rule, I'm not sure how Carey viewed the Burleson play differently than the NFL viewed Johnson's noncatch last season. Maybe we'll learn more after the game.

StaffordWatch: Lions quarterback Matthew Stafford had a great start to this season, but Sunday was probably his worst game of the year. He was sacked five times, including once for a safety, and looked tentative in the pocket thereafter. I didn't like how many sidearm passes he threw, which told me he was trying to squeeze the ball into too-small targets, and had at least two balls slip from his hand in the pocket. Consider it a learning experience.

Ford FieldWatch: By my count, the 49ers had five false-start penalties on offense. That brings the two-game total at suddenly raucous Ford Field to 14. There were some nervous moments Sunday in Detroit, but the numbers are the numbers.

What's next: The Lions will host the Atlanta Falcons at Ford Field.