Birthday boy Owen Farrell gave a clenched fist salute after nailing the last-gasp kick which gave Saracens a sensational win.
Trailing by 12 points with four minutes left the five-time Premiership champions looked dead and buried.
Saracens boss Mark McCall even admitted the game had “gone” after a “horrible period” either side of half-time in which his side shipped 26 unanswered points.
But captain Farrell, 31, refused to allow his team to roll over and twice led them back up the field for tries - both of which he converted from wide out.
“We showed some proper fight at the end,” said the England star. “It’s a good feeling to win, especially like we did."
Saracens were indebted to their bench, Jackson Wray providing a major energy boost and Tom Woolstencroft the two late tries from mauls. But to break Gloucester's hearts it still needed Farrell to hold his nerve.
“I knew Owen was going to kick it," I’d packed my bags at that point,” said Kingsholm boss George Skivington.
“He lives for those moments,” agreed McCall. “He’s done it time and time again.”
There seemed no way back for last season’s beaten finalists as Gloucester, playing their hearts out for team mate Ed Slater up in the stands, bagged a bonus point with more than half an hour to spare.
Saracens had opened the scoring through Max Malins before Slater, diagnosed with motor neurone disease in July, was introduced to the crowd to rapturous applause.
Gloucester immediately hit back, as if inspired by Slater's appearance on the big screen. The first of super sub Val Rapava-Ruskin’s two tries was a portent of what was to come, the away pack mauling the prop over.
Although Ben Earl quickly restored Sarries’ advantage, Gloucester stayed in the contest and pulled to within a score on the stroke of half-time.
This time it was Albert Tuisue cashing in on their maul power and four minutes after the restart the visiting pack were at it again, this time for Chris Harris to score out wide.
When Adam Hastings beat Earl one-on-one to claim the bonus point score two minutes later and Rapava-Ruskin made it four tries in 13 minutes that should have been that.
But nobody told Farrell. Or if they did he wasn’t having any of it.
SARACENS - Tries: Malins, Earl, Hallett. Cons: Farrell 2, Daly. Pens: Farrell 2.
GLOUCESTER - Tries: Rapava-Ruskin 2, Tuisue, Harris, Hastings. Cons: Hastings 4. Pens: Hastings 2.