The 2011 league champions fought back magnificently from a six-point interval deficit at Allianz Park to prevail 31-17 as Kelly Brown, Brad Barritt and Chris Ashton scored tries.
Fly-half Owen Farrell chipped in with 16 points from the boot as Saracens' second-half masterclass underlined a rude state of health building towards next Saturday's Heineken Cup final showdown against holders Toulon in Cardiff.
But there was also a major injury scare for England head coach Stuart Lancaster as Quins full-back Mike Brown limped off nursing a suspected hamstring injury midway through the second period.
Brown and wing Ugo Monye scored Quins' tries - Nick Evans added a penalty and two conversions - but Brown's early exit will mean an anxious wait for Lancaster, who is already resigned to being without players from Saracens and Northampton for England's opening Test against New Zealand in Auckland on June 7.
The possible loss of Brown - this season's RBS 6 Nations player of the tournament - is a potential hammer-blow for England, and Quins shared his pain as their season reached its conclusion.
At times, it was far from plain sailing for Saracens, who were briefly reduced to 13 men when centre Marcelo Bosch and prop Matt Stevens received yellow cards in quick succession, and they trailed 17-11 at half-time.
But 20 unanswered second-half points showcased their quality, and they will now contest a second Premiership final after winning domestic silverware three years ago.
Saracens suffered a late blow when their England international lock Mouritz Botha was injured during the warm-up. Alistair Hargreaves replaced him, with Eoin Sheriff going on to the bench.
Quins, though, had no such dramas as they paraded a team led by their current England quartet of Brown, Chris Robshaw, Danny Care and Joe Marler.
Evans and Farrell exchanged early penalties, before referee Wayne Barnes found himself having to make a key early decision following Saracens hooker Schalk Brits' tackle on Quins prop Kyle Sinckler.
Sinckler jumped into the tackle as Brits' momentum took Sinckler into a horrible head-first landing, but Barnes and television match official Graham Hughes correctly ruled it was not an illegal hit and no sanctions were administered.
A second Farrell penalty edged Saracens ahead, yet they quickly found themselves reduced to 13 men after Bosch and Stevens departed within four minutes of each other.
Bosch received a yellow card for a dangerous tackle on Evans, then Stevens, who was making his final home appearance before joining Natal Sharks this summer, left the action following a deliberate knock-on.
Quins needed to press home their numerical advantage, and they kept cool in stamina-sapping sunshine, moving through several phases of play before an unmarked Monye was able to walk over for the game's opening try.
Evans added the conversion, but Saracens, despite being two players short, hit back superbly just before Bosch returned as slick handling enabled Scotland flanker Brown to crash over against a stretched Quins defence.
It meant that Saracens led by a point as half-time approached, yet it proved a short-lived advantage as Quins capitalised on poor midfield play and collected an opportunist try.
A powerful Tim Molenaar tackle caused Saracens to spill possession, and Robshaw's kick ahead was gathered by Brown for the visitors' second try.
Evans' conversion took Quins clear at the break, setting up an intriguing second 40 minutes as Saracens faced a major fight to keep alive their double dream.
Saracens' goalkicking woes continued, though, with Farrell and Bosch missing penalties in quick succession immediately after the break. It meant the home side had blown 14 possible points from the tee inside 50 minutes.
But they regained the lead after some weak Quins defence allowed Barritt to smash his way through initial attempted tackles by Evans and Molenaar before he touched down near the posts.
Farrell's conversion and a subsequent penalty made it 21-17, yet just when Saracens looked as though they might have made the game safe as Bosch sprinted clear, Barnes ruled it out for offside.
But Saracens still had plenty left in the tank, and Ashton's 62nd-minute touchdown - complete with a trademark celebratory dive - sealed the deal.
- Sports & Recreation
- Owen Farrell
- Kelly Brown
- Nick Evans
- Marcelo Bosch
- Chris Ashton