It came down to trust.
The final minutes had unfolded at a dizzying pace. Fourteen seconds remained. San Francisco trailed New Orleans 32-29 and faced third-and-4 from the Saints' 14-yard line.
New Orleans was in zone coverage with two safeties back. Vernon Davis was in the slot left, Alex Smith in the shotgun. The ball was snapped, and Smith started his delivery before Davis, running straight downfield, even cut inside. Smith was throwing to a spot he trusted Davis would reach before Roman Harper.
Smith trusted his arm. He trusted his read. He trusted his offensive line. He trusted Davis.
And perhaps more telling than anything, 49ers coach Jim Harbaugh trusted Smith enough with the season on the line, in the red zone, where a mistake could end it all, to go for the win rather than play it safe for the tie and try again in overtime. Smith delivered the ball at just the right time, a split-second before Harper could get to Davis, who made the catch at the goal line to win the game.
Think about it. Harbaugh put the ball in Smith's hands and said, "Go win this," even though all season Harbaugh had asked Smith to be the caretaker of the 49ers' offense, to not make mistakes, to not turn it over, to let the defense and the run game and the spectacular special teams carry the load.
It was a fantastic catch by Davis, there is no doubt, but it was a better throw by Smith.
"He looked like Joe Montana," Ron Jaworski said on Tuesday while watching the coaches' tape of the game at his office at NFL Films. "Eventually, you have to make plays. I think in this game he actually made plays that won the game for them. Alex Smith won the game, not Alex Smith by not making mistakes. His performance won the game for them."
Since San Francisco selected him No. 1 overall in the 2005 draft, Smith has endured a parade of head coaches and offensive coordinators. Not since his second season, when Norv Turner was the Niners' offensive coordinator, has Smith had a teacher like Harbaugh. A former NFL quarterback, Harbaugh understands the nuances of the position. He sees what Smith sees. And clearly the two have developed a mutual trust in each other.
That was on display late in the game Saturday.
On Tuesday, I watched the game film first with Greg Cosell, the long-time executive producer of ESPN's "NFL Matchup," then with Jaworski. Both said Smith's play in the final four minutes of the game was a gigantic step in his maturation process, and that he made three throws that were as technically sound as any top quarterback in the NFL could make. They were throws, both men noted, that Smith had not been asked to make all season.
The first play came with 3:14 left. New Orleans had just taken its first lead of the game (24-23) on a 44-yard Darren Sproles reception. On second-and-10 from the San Francisco 33-yard line, Davis was split left, the lone receiver on that side, with two receivers on the right. The Saints were in cover-zero, an aggressive formation Cosell pointed out they played on about 10 snaps, with Malcolm Jenkins on Davis in man coverage. It was a matchup San Francisco undoubtedly liked, given the tight end's speed against the slower safety.
With a blitz coming, Smith dropped back and started his throwing motion before Davis had run 10 yards. He quickly lobbed the ball 37 yards and it fell over Davis' shoulder and into his hands for a huge gain. Three plays later, on a called quarterback run, Smith rushed 28 yards around left end and got huge blocks by wide receiver Kyle Williams on the edge and left tackle Joe Staley downfield to score a touchdown.
After the Saints answered to regain the lead, 32-29, with less than two minutes to play, New Orleans opened the 49ers' ensuing drive in its prevent defense. But Smith completed two check downs to Frank Gore, forcing the Saints back to their man-to-man.
Three plays later, with the Saints dropping eight in coverage and rushing three, Smith hit Davis again to win the game.
"It's absolutely precise," Jaworski said. "That three-man rush made it a really hard throw."
During the regular season, San Francisco ranked 30th in red zone offense, scoring just 22 touchdowns in 54 appearances (40.7 percent). By comparison, the New York Jets scored touchdowns on 65.5 percent of their red zone appearances.
But according to ESPN Stats and Information, Smith now has thrown five red zone touchdowns to Davis on nine targets, including the playoffs.
Against New Orleans, the Niners were 2-of-4 in the red zone and called 18 pass plays and 11 runs on first down. They were more aggressive in this game, with Smith completing nine passes on first down. On the last two drives, Smith was 7-of-9 for 135 yard and a touchdown.
Cosell has watched every throw Smith has made this season. He said he always thought Smith was "limited" as a passer because he had "technique flaws in his delivery that prevented him from driving the ball at the intermediate and deeper levels." He also thought Smith had "a bit of windup" to his throwing motion that limited him when the pocket collapsed.
With Harbaugh running an offense that suited Smith, Cosell saw Smith's confidence grow during the season. But before Saturday, he still didn't think Smith could make the big-time throws in critical moments of a game like he did against the Saints.
"He made throws in game-deciding situations," Cosell said. "Do I now think he's Drew Brees or Tom Brady? No. But I think given that he got into that situation in a critical game and he made those throws, you've got to give him credit for that. Those were not easy throws. Those were NFL throws you have to make in this league to be a higher-level quarterback. He didn't have to do that this year."
Smith will have to do it again Sunday, when San Francisco hosts the New York Giants in the NFC Championship Game. Unlike New Orleans, the Giants, as Jaworski noted, will bring pressure with their aggressive front four. How Smith handles it will be a key to the game.
"He reeks of confidence right now," Jaworski said of Smith. "If there's a throw that validates that feeling, it was that game winner. I haven't seen that throw all year. In fact, that was one of my concerns going into the game. I thought New Orleans had a huge advantage in the red zone because the 49ers were settling for too many field goals.
"In that area, you have to anticipate so well and you have to trust your receivers and trust yourself, and that's exactly what that play was."
Ashley Fox is an NFL columnist. Follow her on Twitter: @AshleyMFox.