Saracens centre Marcelo Bosch landed a match-winning penalty with the final kick of the game to guarantee English representation in the semi-finals of the Champions Cup.
Bosch stepped up to take the 55-metre shot at goal after Racing Metro replacement Fabrice Metz had been penalised for diving over the top with only 10 seconds remaining on the clock.
The kick was at a slight angle and into the wind, but the Argentinian nervelessly steered his attempt between the uprights to seal a 12-11 victory and was immediately mobbed by his team-mates as the final whistle sounded.
As a precaution, referee Nigel Owens and his touch judges were escorted from the pitch by security as boos rang out in protest at the Welsh official's decision to penalise Metz.
The Stade Yves-Du-Manoir had rubbed its eyes in disbelief as Saracens led 6-5 at the interval despite having been pummelled throughout a one-sided first half.
Last season's runners-up had summoned upon their reserves of character and experience of knockout European rugby to stay in contention as the showdown entered a decisive final 10 minutes.
Fly-half Charlie Hodgson kicked one penalty and full-back Alex Goode supplied six points to keep the match favourites in sight.
Two second-half penalties from scrum-half Maxime Machenaud, who also crossed for the game's only try in the 27th minute, placed Racing in control that the Parisians only relinquished as Owens was preparing to blow for full time.
Saracens' victory has set up a last-four showdown with Clermont in St Etienne in two weeks' time.
Saracens drew first blood with a Hodgson penalty, but it was Racing who showed a sharper edge in attack with Wales centre Jamie Roberts prominent as they found early openings.
Goode was lucky to escape punishment for blocking Teddy Thomas as the Top 14 club continued to pour forward and only the failure to ground properly prevented hooker Dimitri Szarzewski from scoring.
Saracens' pack had splintered before the line-out catch and drive that led to the chance for Szarzewski and Racing's control continued as Roberts bulldozed a path through the black shirts.
An interlude of Saracens probing for the line was brief and in their next attack Racing scored, Machenaud ending another rolling maul by darting between several defenders to dive over.
With lock Jim Hamilton in the sin-bin for bringing down a maul and Hodgson missing a pair of penalties in quick succession, the Premiership title challengers were contributing to their downfall yet still trailed only 5-3 on the scoreboard.
Brice Dulin renewed Racing's assault from full-back by capitalising on some feeble defending only for another promising move to end when Roberts failed to roll away.
Yet Saracens' tenacity and a second Hodgson penalty meant they entered half-time 6-5 up and their lead was extended to four points when Goode steered the ball between the posts.
Wing Juan Imhoff spilt the ball forward while being tackled by Bosch when all he needed to do was fall over the line as Racing launched a rapier-like counter that ultimately ended with three points from Machenaud.
A gliding break from Goode put Saracens back on the front foot but expert defending saw him relieved of the ball and a nerve-jangling final 10 minutes awaited when Machenaud kicked his second penalty.
It ended with Bosch completing a challenging kick under high pressure to the delight of the travelling fans.