New York Giants will face New England Patriots in the Super Bowl after dramatically beating San Francisco 20-17 in overtime.
Two glaring errors by rookie punt returner Kyle Williams proved fatal for the 49ers.
Lawrence Tynes, who was born in Greenock, Scotland, kicked the winning field goal from 31 yards.
Giants will face the AFC-winning Patriots who beat the Baltimore Ravens 23-20 in another thrilling encounter.
Super Bowl XLVI, to be held in Indianapolis on 5 February, will be a repeat of the 2008 Super Bowl in which the Giants upset the Patriots 17-14.
New York are again likely to be underdogs, but that will only suit quarterback Eli Manning, who seems to reserve his best form for the big occasions.
But it will be another big-time player who will always be wondering what might have been.
Vernon Davis's two spectacular touchdowns ultimately proved insufficient. But for a long time the San Francisco tight end's catches - for 73 and 28 yards from quarterback Alex Smith - had the raucous home crowd dreaming of glory.
While Tynes will be the toast of the Big Apple, another kicker, the Ravens' Billy Cundiff will share Williams's despair.
With seconds remaining, the Baltimore kicker had a routine opportunity to force overtime, but hooked his 32-yard attempt horribly left.
Even before his miss, however, the visitors had a great chance to secure victory but wide receiver Lee Evans dropped quarterback Joe Flacco's pass in the endzone.
The game started slowly before a superbly executed seven-yard run from the Patriots' BenJarvus Green-Ellis gave the hosts a 10-3 lead.
Baltimore hit back through Flacco's six-yard pass to tight end Dennis Pitta in the endzone but with three minutes remaining, Gostkowski booted a 35-yard field goal to give New England a 13-10 lead at the break.
The second half began as the first ended, with the Patriots having to settle for another field goal, this time from 24 yards, after another stop in the red zone by Baltimore's rapidly improving defence.
Then, after a hugely impressive drive in which they converted three third downs to advance to the New England 29-yard line, the Ravens' speedy wide receiver Torrey Smith caught a short pass and raced down the right-hand touchline into the endzone.
Things got even worse for the Patriots when Danny Woodhead fumbled the kick-off return, before Cundiff's 39-yard field goal made it 20-16 to the visitors with 50 seconds of the third quarter remaining.
But Patriots' quarterback Tom Brady, who has already won three Super Bowls with the Patriots, leapt into the endzone two plays later to restore the Patriots' lead.
Trailing 23-20 with less than eight minutes remaining, the Ravens then suffered their first turnover when Flacco's pass was intercepted by linebacker Brandon Spikes.
Brady went for the jugular by throwing a long bomb towards the Ravens' endzone but it was a gamble that backfired spectacularly as first Bernard Pollard tipped the ball before Jimmy Smith somehow scooped it up inches from the turf.
Ultimately though, it was not enough and the Patriots will go to Indianapolis knowing that this could, yet again, be their year.
In the Giants-49ers game, the home side got off to the best possible start when Davis - the hero of last weekend's spectacular late victory over the New Orleans Saints - raced into the endzone.
The Giants equalised in the second quarter when Manning capped a fine 10-play drive with a six-yard touchdown pass to tight end Bear Pascoe.
And they went into half-time with a 10-7 lead, courtesy of Tynes' 31-yard field goal, after an impressive two-minute drill by Manning.
After the break both defences were on top before Davis caught another perfectly thrown touchdown pass from Smith with five minutes remaining in the third quarter.
The Niners' defence then tightened its grip, despite the best efforts of Manning and his outstanding wide receiver Vernon Cruz, who caught 10 passes for 142 yards.
Then came the first error by Williams, only playing because of injury to the 49ers' first-choice return man, when he inexplicably allowed a punt to brush against his leg in the fourth quarter.
While his glancing touch was missed by the officials on the field, video evidence was used to overturn the decision and give the Giants the ball back.
Manning took full advantage. Despite facing a third-and-15 situation, he threaded a perfectly thrown pass to Mario Manningham in the endzone for a 17-yard touchdown to give the Giants a 17-14 lead with 8.34 left.
San Francisco recovered to level the scores, courtesy of a 25-yard field goal from David Akers, with 5.39 remaining.
No further scoring opportunities meant overtime. Possessions were traded before Williams' second blunder - a fumble - finally killed the Niners' dreams.