SAN FRANCISCO -- The New York Giants have their own Super Bowl formula: in overtime and on the road.

And with Lawrence Tynes' foot.

Five plays after the 49ers' Kyle Williams fumbled a punt, Tynes kicked a game-winning 31-yard field goal in overtime, sending the Giants to the Super Bowl with a 20-17 victory over San Francisco in the NFC Championship Game on Sunday.

In another tight one in this decades-old postseason rivalry, both defenses made key stops before New York capitalized on a rare mistake in San Francisco's resurgent season. Williams' blunder put the Giants in perfect position for another sensational finish in a season full of them.

"That was a tough game. We had to fight for every yard that we got," Giants quarterback Eli Manning said. "Defense was outstanding, special teams getting us two turnovers was huge. That led to 10 points."

The first three overtime series ended in punts before Williams fumbled. The Giants won it moments later and silenced -- for good this time -- the towel-waving, poncho-wearing sellout crowd at cold, rainy Candlestick Park.

"It was one of those situations where I tried to turn it upfield and it just didn't work out," Williams said.

Manning and the Giants (12-7) will face the New England Patriots in the Super Bowl on Feb. 5 in Indianapolis as 3½-point underdogs. The last time the teams met for the NFL title, 2008, the Giants ended the Patriots' bid for a perfect season.

Tynes had a hand, er, foot in getting the Giants to that one, too, kicking the game-winning field goal in overtime.

Devin Thomas put the Giants in position this time by recovering his second fumble of the game after Jacquian Williams stripped the ball from fill-in return man Williams, who also fumbled earlier to set up a New York touchdown.