Super-sub Paul Grayson kicked Northampton into their first European final with a dramatic injury-time penalty that killed off Llanelli's heroic Heineken Cup challenge.
Former England fly-half Grayson, dropped for a pulsating semi-final showdown, came off the bench and struck gold four minutes into stoppage time.
He had performed a similar feat against Wasps in the last eight, but rarely can he have experienced a pressure kick of such significance.
His 84th-minute penalty took Saints into the Heineken Cup final against Irish provincial champions Munster - conquerors of Toulouse yesterday - at Twickenham on May 27.
And it completed a stirring Northampton fightback, having trailed 19-9 at the break.
Grayson only took over the kicking duties when England captain Matt Dawson, who had slotted six penalties, left the Madejski Stadium action five minutes from time.
Northampton didn't even go ahead until England wing Ben Cohen crashed over for a 70th-minute try, but their resilience and magnificent defence was worth the entrance money alone.
Llanelli had their own goalkicking hero in Wales fly-half Stephen Jones - he landed seven penalties and a conversion of centre Dafydd James' first-half try - but Northampton dug deep when it really mattered.
Llanelli's travelling support - a 10,000 Scarlets army - painted Reading red, easily out-numbering the Northampton following among a 15,000-strong crowd.
But it was the Saints who made a more decisive start when Wales centre Allan Bateman put full-back Nick Beal clear in space, only for Scarlets centre Neil Boobyer to pull off a crunching tackle.
Early exchanges were inevitably fast and furious, yet once Llanelli settled, Saints found themselves under increasing pressure.
A concerted attack took the Welsh side agonisingly close to Northampton's line, and when Saints hooker Federico Mendez strayed deliberately offside, Jones struck from 15 metres.
Dawson had missed a penalty chance from 45 metres, then Jones again showed him how it should be done, slotting his second penalty for a 6-0 lead after 14 minutes.
Dawson's big-match temperament didn't take long to surface though, booting a 19th-minute penalty when Llanelli strayed offside, and adding another three points minutes later after Scott Quinnell set off on a rampaging midfield run, but he killed possession in the tackle.
Despite the glorious weather and a perfect playing surface, errors abounded on both sides, but Llanelli looked a more cohesive and creative unit.
Jones and Dawson exchanged further penalties, but eight minutes before the break, persistent Llanelli pressure reaped its reward.
A long pass from Jones sent strong-running James blasting through the weak combined defensive efforts of Pat Lam and Beal, and Llanelli's hordes celebrated.
The immaculate Jones converted from the touchline, and followed up with a stunning 50-metre penalty, putting Llanelli 10 points ahead at half-time.
Saints boss John Steele made a change during the break, replacing Wales Under-21 lock Andy Newman with Jon Phillips as Northampton set about stopping another trophy slipping away.
Already out of the Premiership title race, Saints' European glory hopes hinged on a massive second-half effort.
Early signs were encouraging. Just three minutes in, Dawson found fly-half Ali Hepher, Beal took the move on, floated out a pass and Bateman finished things off.
Dawson couldn't convert, but then kicked a 50-metre penalty after an ugly incident involving Llanelli prop Phil Booth.
The Scarlets loosehead launched an unproved attack on Saints' England forward Tim Rodber, landing four punches, and Irish referee Alan Lewis sin-binned Booth, although he could not have complained had the card been red instead of yellow.
Temporarily reduced to 14 men, Llanelli sent on replacement prop Martyn Madden - they took off flanker Ian Boobyer - and Jones nervelessly kept going about his business.
Two more penalties during four minutes of Scarlets dominance took Llanelli 25-17 in front as Northampton struggled to make their advantage count.
Just as Booth returned, Saints reduced their arrears.
Referee Lewis had already penalised Llanelli for offside when Quinnell stiff arm-tackled Dawson. Quinnell avoided punishment, but Dawson dusted himself down to kick the penalty.
Llanelli, with Wales lock Chris Wyatt punching huge holes in Northampton's defence, put increasing width on the game, yet unforced handling errors continued to thwart their try-scoring efforts.
Another Dawson penalty, his sixth, spurred Northampton and ensured a nerve-tingling final 15 minutes with only one score between two well-matched sides.
Northampton dramatically went ahead for the first time with just 10 minutes remaining.
Marvellous approach work from outstanding Saints flanker Rodber stretched Llanelli's defence, and Cohen displayed considerable strength to break Wyatt's tackle and touch down wide out.
The Scarlets responded immediately, scrum-half Rupert Moon storming upfield, and it took a try-saving tackle from Beal on Cardey to keep Northampton in front.
Dawson subsequently left the action, and Llanelli's all-out attacking onslaught almost saw their Tongan wing Salesi Finau - a constant threat - score near the corner.
Northampton could not escape from their 22 as the Scarlets stepped up a gear in search of their Holy Grail.
As the tie moved into injury time, Llanelli were awarded a penalty, undoing monumental Northampton defensive work, and Jones made no mistake, levelling it at 28-28.
But four minutes into injury time, Grayson came up trumps from 48 metres, and Northampton were home in quite breathless fashion.Reuse content