A run of 17 unanswered second-half points saw Gloucester hand Saracens only their second defeat of the season with a 23-17 Premiership win at Kingsholm.
Sarries went into Friday's clash without the services of Owen Farrell and Maro Itoje, both on international duty with England.
Alex Lozowski and George Kruis, both dropped by England coach Eddie Jones, featured in Mark McCall's XV, but the leaders still came unstuck, much to the delight of a vociferous home crowd.
Billy Twelvetrees kicked 13 of Gloucester's points while Ollie Thorley and Tom Hudson crossed, moving them at least temporarily up to third in the table.
Twelvetrees and Lozowski traded early penalties, with the boot of the latter putting Saracens 9-3 to the good at the interval.
The gap was narrowed by a second Twelvetrees penalty, however, when Schalk Brits went over for Sarries after a break from Vincent Koch the writing appeared to be on the wall.
Lozowski missed the drop-goal conversion, showing the presence of mind to take it quickly before the officials could look into a possible obstruction in the build-up.
But Gloucester responded magnificently, with Ben Vellacott's break moving them inside Sarries' 22 before Billy Burns found Thorley with a superb chip kick to the corner.
That was soon followed by Hudson marking his first Premiership start with a try, Twelvetrees converting to make it a nine-point gap that ultimately proved insurmountable.
Ben Spencer had a try ruled out as he was adjudged to have been short of the line by the TMO and Lozowski skewed a penalty wide with five minutes left.
Sarries did at least secure the consolation of a losing bonus point, Spencer knocking over a three-pointer, but that was little more than a footnote on a night belonging to Gloucester.
