The play was reviewed and upheld. If Kaepernick had maintained possession, the 49ers could have used their final timeout to try for the touchdown again, or attempt a field goal to tie.
"I just went to kind of meet him head to head down there and as I'm going down, I just see the ball sitting there," said Laurinaitis, who came out of the pile with the ball.
On third-and-goal from the 1, Kaepernick bobbled the snap, controlled it and dove between his blockers as fullback Bruce Miller tried to shove him into the end zone. Kaepernick fumbled as he went down in the mass of bodies, apparently short of the goal line.
"On the last play it went into a pile, and there was nothing we could see that could change the ruling on the field," referee Jerome Boger said.
The Rams, 9 1/2-point underdogs to start the week, never let Kaepernick get comfortable. The quarterback spent more time on his backside and running from St. Louis defenders than he did directing the offense.
Then, the crazy final play of the first half was upheld on replay review.
As the two teams headed for their respective locker rooms, the head coaches stayed put for the ruling, which was that forward progress was stopped in the field of play and the play stood without a safety.
Kaepernick threw an earlier 27-yard touchdown pass to Boldin, giving him TD passes in 15 straight games - tied for the second-longest streak in franchise history with Jeff Garcia. Hall of Famer Steve Young had 17 in a row.
When the NFC West rivals first played Oct. 13, Kaepernick threw for 343 yards and three touchdowns with no interceptions or sacks. He finished Sunday with 237 yards on 22-of-33 passing.
San Francisco struggled to get pressure on Davis, while missing star linebacker Patrick Willis for the second straight game with an injured left big toe.
Copyright 2014 by The Associated Press