A second-half surge from Saracens shattered Saints’ chances of appearing in next Sunday’s LV= Cup final at Franklin’s Gardens.
An excellent individual effort from wing Mike Ellery a minute after the restart, allied with some tidy kicking from scrum-half Ben Spencer secured a 24-20 success for Sarries.
Jim Mallinder’s men had put themselves in a good position to progress after 13 points from fledgling fly-half Sam Olver sent them in at the break with an eight-point cushion.
But Saracens responded superbly after the interval and, despite a Lee Dickson try 15 minutes from time, the home side had enough to get to the Gardens.
Saints had won an Aviva Premiership fixture at Allianz Park back in November, when a dominant first-half display laid the foundations for a 31-24 win.
And they started strongly again in the bid to secure an LV= Cup semi-final victory, with the men in lime bossing the opening stages of the encounter.
Saracens prop Rhys Gill had drowned under the weight of the Saints pack in the league fixture in November and he was soon submerged in this scrum battle, with Salesi Ma’afu’s muscle earning a couple of early penalties.
Olver attempted to use his side’s early territorial advantage with a drop goal, but having failed with that effort he soon secured an early lead with a well-struck penalty.
Saints were firmly in the ascendancy, with Saracens struggling to get out of their own half, and Olver soon doubled the lead from the tee.
Such was their dominance that the away side could easily have been further ahead, and they almost were as Tom Collins charged towards his own kick, only to narrowly miss out at the last.
Saracens had posed little attacking threat in the opening 20 minutes, but they were to score with their first real attack of the game.
Speedy wing David Strettle ran a clever line and finished off a slick Sarries move, punching the flag after scoring in the corner.
Spencer missed the conversion and Saints were soon at their door again with good work from Samu Manoa and Phil Dowson helping to release Olver for a tidy score.
The 20-year-old capped the special moment of a first senior try with the easy conversion and his team had an eight-point lead they merited.
Maro Itoje tried to wrest back some momentum Saracens with a huge hit that left Olver winded before Saints full-back Ahsee Tuala made a crucial tackle to stop Itoje in his tracks.
The home side’s skipper was looking menacing and Sam Dickinson was soon making a superb try-saving tackle to stop him crossing in the corner.
Dom Waldouck was next to make a key stop as he forced Spencer into touch, with the TMO needed to confirm the Saracens man had not scored.
Saints had managed to hold out during a sticky finish to the first half, but it was to take just a minute for their resistance to be broken in the second.
Ellery waltzed through for a superb solo score and Spencer’s successful conversion cut the gap to just a single point.
And Saracens were soon ahead as Spencer’s penalty from wide left put them in front for the first time in the match.
Saints needed to regain the momentum, but Spencer was soon sticking the boot in again, putting the home side five points up.
Mallinder’s men were leaking penalties at an alarming rate, and yet another Spencer effort meant they were starting to need to scale a mountain rather than a molehill.
But the introduction of Calum Clark, Stephen Myler and Dickson helped turned the tide and it was the scrum-half who was to grab a score that got his team back in the game.
Dickson dotted down after a big lineout drive from the forwards and Myler narrowed the gap to a point with 14 minutes to go.
Saracens were soon back on the front foot, with Nils Mordt making the most of a spell of sustained pressure to land a drop goal, leaving Saints with it all to do in the final eight minutes.
And, despite a valiant late charge which took them into the home 22, Mallinder’s men couldn’t get over the line, ending their hopes of LV= Cup glory.
Saracens: Ransom; Ellery, Bosch, Streather, Strettle; Mordt, Spencer; Gill (Barrington 52), Saunders (Spurling 52), Figallo (Alo 72); Itoje (c), Smith (Kruis 25); De Jager, Hankin (Brown 67), Joubert.
Replacements: Whiteley, Palamo, Fercu.
Saints: Tuala (Wilson 72); Elliott, Stephenson, Waldouck, Collins; Olver (Myler 61), Fotuali’i (Dickson 61); Corbisiero (E Waller 62), Haywood (Williams 72), Ma’afu (Denman 56); Manoa, Ryder (Nutley 72), Dowson (c), Fisher (Clark 56), Dickinson.
Referee: Dean Richards