NFC West Week 10 decisive moment

Fourth down, 18 yards to go.

San Francisco 49ers trailing the St. Louis Rams, 17-13, with 2:23 remaining in regulation at Candlestick Park.

Troy Smith at quarterback for San Francisco from the Rams' 39-yard-line.

"Kind of an ad-lib situation," Smith said after finding Frank Gore uncovered near the left sideline for a 23-yard gain.

The improbable play set up the 49ers' go-ahead touchdown, helping them to a 23-20 overtime victory.

"Frank being the player that he is, the year-in, year-out, vet leader that he is, definitely just let me know, putting a bug in my ear as far as when we were breaking the huddle, some of the things that he would ad-lib if it happened," Smith said. "It just so happened that it happened that way, and we were going up the sideline."

Smith had found Gore for a 14-yard gain on third-and-32, so it's not as though the Rams should have been surprised when Smith targeted Gore again on the next play.

The 49ers should have been reeling after left tackle Joe Staley, playing on a badly injured leg that was either broken or about to break, committed penalties on back-to-back plays -- the latter infraction wiping out a 43-yard touchdown pass to Vernon Davis. Gore's receptions, followed one play later by Smith's 16-yard scoring pass to Michael Crabtree, gave the 49ers life.

"There is nothing more frustrating," Rams coach Steve Spagnuolo said. "You never relax and all that. Again, a good quarterback got it to a really good back twice. I’m sure the defensive guys would say the same thing. There is no excuse. That can’t happen."