|Northampton (13) 24|
|Tries: Penalty try, Wood Con: Myler Pens: Myler 4|
|Saracens (13) 29|
|Tries: Strettle, George Cons: Farrell 2 Pens: Farrell 5|
Saracens reached the Premiership final after beating Northampton in a pulsating match at Franklin's Gardens.
Owen Farrell's late penalty secured victory over Saints, who had finished the season at the top of the table.
David Strettle's converted try gave the visitors the lead but the 2013-14 champions levelled by half-time.
Jamie George's try helped Saracens carve out a five-point lead and they held on to reach Twickenham where they will face Bath on 30 May.
The Blue, Black and Whites beat Leicester Tigers 47-10 in the other semi-final at the Rec.
Mark McCall's Saracens only secured their play-off place on the last day of the regular season and they are into the Premiership final for the fourth time in six seasons.
Northampton had won both league meetings between the two sides this season, and beat Saracens in extra-time to lift the Premiership trophy for the first time in their history last May.
But it was the north London side who went ahead when Strettle kicked down the touchline and, with Saints full-back Ahsee Tuala out of position receiving treatment, Duncan Taylor outpaced Lee Dickson to chase down the loose ball and fed Strettle, who crossed in the corner.
Northampton's pack drew the home side level with a penalty try as Sarries were repeatedly penalised and had prop Mako Vunipola sent to the sin-bin.
With Saints dominating possession and territory, Saracens relied on the boot of Farrell to twice give them a three-point lead, but Northampton fly-half Stephen Myler replied to level the scores on the stroke of half-time.
A Myler penalty early in the second period gave Northampton the lead for the first time but George drove over to restore the away side's advantage.
Saints hit back as Tom Wood touched down from a rolling maul but crucially Myler missed the conversion, which gave Saracens a two-point advantage heading into the final 20 minutes.
Farrell extended that lead to 26-21 with a penalty and Saracens then managed to soak up pressure from Northampton's forwards.
Farrell kicked his fifth penalty of the afternoon to take Saracens two scores clear with three minutes left and, although Myler replied, Saracens saw out the final minute without alarm to secure their place at Twickenham.
Northampton director of rugby Jim Mallinder:
"We knew what their plan would be and they did what we expected, but they do it very, very well.
"At the breakdown they were physical.
"Those Vunipola brothers....once they get over the ball their stomachs are touching the ground already. It's near impossible to move them.
"Everyone decides how they want to play and Saracens have gone down their route. To become champions you have to beat all styles and we didn't get over this hurdle."
Saracens director of rugby Mark McCall:
"We had a mass of sickness around the squad this week. Schalk Brits was in hospital for two days and lost seven or eight kilograms.
"There were 10 other people who had it, but you wouldn't have known. You add the bug to the occasion and it tells you the sort of group we have.
"That was us out there hunting people down, getting off the floor to make tackle after tackle. It was a performance to be proud of.
"That was a Titanic semi-final of unbelievable intensity and we're thrilled to come out on the right side of it."
Northampton: Tuala; K. Pisi, G. Pisi, Burrell, Elliott; Myler, Dickson; Corbisiero, Hartley (capt), Ma'afu, Lawes, Day, Wood, Clark, Manoa.
Replacements: Wilson for Tuala (3), Waller for Corbisiero (32), Stephenson for Wilson (41), Fotuali'i for Dickson (51), Denman for Ma'afu (53), Haywood for Ashton (68), Fisher for Day (69), Dickinson for Clark (75).
Saracens: Goode; Wyles, Taylor, Barritt, Strettle; Farrell, Wigglesworth; M. Vunipola, George, Du Plessis, Kruis, Hargreaves (capt), Itoje, Burger, B. Vunipola.
Replacements: Figallo for Du Plessis (59), Ashton for Strettle (59), Hamilton for Hargreaves (62), Wray for Itoje (65).
Not Used: Saunders, Barrington, de Kock, Hodgson.
Sin Bin: M. Vunipola (12)
Referee: Greg Garner (RFU)