Maxime Machenaud looked set to be the match-winner for the Top 14 side after he scored the only try of the match in the first half before kicking two penalties after the break to edge the Paris outfit in front.
However, with just seconds of the 80 minutes remaining, Saracens were awarded a penalty. The distance was too far for Alex Goode in the wind meaning Marcelo Bosch stepped up and sent the last kick of the game straight between the posts.
Saracens had held a one-point lead at half-time courtesy of two Charlie Hodgson penalties and despite Racing having been the better side, the visitors could have been further ahead – the former England fly-half sending two additional kicks narrowly wide of the posts shortly after Machenaud’s try.
The try itself came immediately after Saracens were reduced to 14 men. With Racing on the drive, Jim Hamilton was adjudged to have collapsed the maul and was sent to the sin-bin.
The hosts went to the corner from the resulting penalty and from the line-out the ball was worked to the scrum-half who crossed to put Racing ahead. Jonny Sexton lined up the kick but was denied by the post and it would prove a costly miss.
Mark McCall’s side extended their lead soon after the break with Goode slotting a penalty as Hodgson received treatment.
The top seeds came back strongly, though, and looked set to score in the 53rd minute as Brice Dulin broke clear. The ball was then worked to Juan Imhoff who lost control of the ball with the try-line at his mercy under pressure from Chris Wyles, although his blushes were spared as the referee judged that the pass to him was forwards.
Racing did close the gap just after the hour mark through the boot of Machenaud and when he kicked another penalty with less than 10 minutes remaining, the hosts were back in front.
The French outfit attempted to run the clock down and managed to do so until conceding a penalty when in possession of the ball and only seconds away from the final whistle.
Bosch did the rest to seal a 12-11 win and spark wild celebrations among the Saracens players and fans alike.