George Pisi scored a hat-trick of tries to help Northampton beat Saracens 26-7 in Saturday's LV= Cup semi-final at Franklin's Gardens.
Saracens dominated the first half and led 7-6 at the interval but were left to rue a number of missed opportunities.
Ben Ransom's first-half try would be the visitors' only five-pointer as Saints came storming back after the break with Samoan centre Pisi touching down three times and Stephen Myler slotting a drop goal to add to Will Hooley's two penalties.
Northampton will now face the winner of Sunday's semi-final between Bath and Exeter in the final.
Tries: G Pisi 2
Pens: Hooley 2
Northampton: 15 Ben Foden, 14 Ken Pisi, 13 George Pisi, 12 Tom Stephenson, 11 Tom Collins, 10 Will Hooley, 9 Kahn Fotuali'i, 8 Sam Dickinson, 7 Phil Dowson (capt), 6 Ben Nutley, 5 Christian Day, 4 James Craig, 3 Tom Mercey, 2 Mike Haywood, 1 Ethan Waller.
Replacements: 16 Ross McMillan, 17 Alex Waller, 18 Gareth Denman, 19 Samu Manoa, 20 Calum Clark, 21 Alex Day, 22 Stephen Myler, 23 Fa'atoina Autagavaia.
Saracens: 15 Ben Ransom, 14 Michael Tagicakibau, 13 Tim Streather, 12 Marcelo Bosch, 11 Jack Wilson; 10 Nils Mordt (c), 9 Ben Spencer, 8 Jackson Wray. 7 Matt Hankin, 6 Justin Melck, 5 Mouritz Botha, 4 Eoin Sherrif, 3 Petrus du Plessis, 2 Jamie George, 1 Richard Barrington.
Replacements: 16 Jared Saunders, 17 Rhys Gill, 18 James Johnston, 19 Hayden Smith, 20 Nick De Jager, 21 Neil de Kock, 22 Charlie Hodgson, 23 Chris Wyles.
Venue: Franklin's Gardens
Referee: Leighton Hodges (Wales)
Assistant Referees: Rhys Thomas (Wales), Kelvin Shorte (Wales)
TMO: Derek Bevan (Wales)