Jaquiski Tartt was his own toughest critic after his dropped interception in the San Francisco 49ers' NFC Championship Game loss to the Los Angeles Rams.

The 49ers led 17-7 going into the fourth quarter, though the Rams soon trimmed that gap to three points with Cooper Kupp's second touchdown catch of the game from Matthew Stafford.

San Francisco looked destined to change the momentum with just under 10 minutes remaining as Stafford uncorked a deep shot intended for Van Jefferson but straight into the arms of Tartt, only for the Niners safety to let the ball slip from his grasp and to the turf.

The mistake did not lead to a touchdown as a Matt Gay field goal tied the game, but the Niners never managed to turn things back in their favour and a late Jimmy Garoppolo interception after another go-ahead kick from Gay gave the Rams victory.

And Tartt offered no excuses as he accepted blame for the agonising defeat.

"For me, it's tough. But it's a moment a lot of athletes I know dream of ... you can make that game-changing play," Tartt told a post-game media conference.

"It was something that I was thinking about all week. I know I can make that play, and the play came up and I ain't make it.

"I know that was a big play of the game, a big opportunity for me and for the team. As a player, I feel like I let my brothers down.

"But for us, we didn't play how we needed to play. ... Obviously my play was a crucial one that I left on the field. Really wish I can have it back, but at the end of the day, take your hat off to the Rams."

Asked what he thought as the ball was coming to him, Tartt replied: "I see it, I'm like 'Oh yeah, he f****d up. We about to win this game,'. It hit my hands. I thought I had it, and I dropped it."

Though Tartt will have nightmares about the would-be interception during the offseason, to lay the blame entirely at his feet would be overly harsh.

San Francisco still had two possessions after Gay's game-tying field goal and lost seven yards across those series as the offense completely collapsed when it most needed to step up and deliver.