A moment of madness by England wing Chris Ashton cost Saracens dear as Exeter Chiefs returned to winning ways at Sandy Park.
After a very disappointing defeat at newly-promoted London Welsh the previous weekend, and at the start of a daunting run of Premiership and Heineken Cup fixtures against some of Europe's best sides, it was important the Chiefs rediscovered their form to avoid finding themselves towards the wrong end of the table.
They had never beaten 2011 league champions Saracens at home before, and the match was on a knife edge at 9-9 early in the second half when Ashton needlessly ran several metres to smash a shoulder charge into the side of a maul close to the Saracens line.
After consulting with touch judge Ashley Rowden, referee Sean Davey – a replacement for David Rose, who was laid low by illness – called for the television match official's help, and after watching the pictures, he had no hesitation in sending Ashton – a summer recruit from Northampton Saints – to the sin-bin for ten minutes.
Four minutes after his departure, Exeter kicked a penalty to the corner and won the line-out, and when they attacked the blindside, replacement scrum-half Will Chudley and winger Matt Jess combined to send Fijian centre Sireli Naqelevuki over in the left-hand corner – where Ashton would have been defending – for his first try of the season.
Even though fly-half Ignacio Mieres missed the difficult touchline conversion, it gave Exeter some welcome breathing space in an intriguing nip and tuck affair dominated by the wet and miserable conditions, and the whistle of referee Davey.
The official was very hot on both sides at the breakdown, and a stream of penalties followed, but at least he was consistent in his decision-making, which is what coaches and players request.
Argentinian Mieres kicked three out of five attempts at goal in the first half, to two out of three by England fly-half Owen Farrell, to give the Chiefs a 9-6 interval lead.
Exeter, though, could, and perhaps should, have been further in front at the end of a first half in which Saracens skipper Kelly Brown was sin-binned for killing the ball at a ruck just short of the visitors' try line.
After nine minutes, fit-again scrum-half Haydn Thomas charged down opposite number Neil de Kock's attempted clearance kick, but after a series of close-range drives, hooker Chris Whitehead unfortunately lost the ball from his grasp with the line at his mercy, and the chance went begging.
Exeter suffered two injury blows to add to a growing casualty list at Sandy Park early in the second period, with Thomas going off with concussion and blindside flanker James Phillips – named in the starting line-up in place of the injured Tom Johnson – helped off the pitch with what appeared to be a right ankle injury.
Farrell levelled the scores with a penalty in the 46th minute, at which point Saracens started to introduce some of their star-studded forward talent off the replacements' bench, such as South African hooker Schalk Brits and former England skipper Steve Borthwick.
Naqelevuki's try opened up a five-point gap on the scoreboard, but that was swiftly closed to two by Farrell's fourth successful kick of the afternoon.
Exeter then lost Whitehead to the sin-bin just before the hour mark, but from the resultant penalty, Farrell was way off target from 35 metres as the weather deteriorated, and the Chiefs' fans could again breathe a sigh of relief.
Saracens kept battering away, but Exeter kept them out, with their defence of the driving maul much improved from their two previous games.
Former England fly-half Charlie Hodgson missed with a 50-metre penalty attempt for Sarries, while winger James Short almost got over in the corner, only to be denied by some fine defence from full-back Luke Arscott, who put in an excellent man-of-the-match performance, closely followed in that regard by former Cornish Pirates prop Carl Rimmer, who did not look out of place, even though he was making his first Premiership start.
With time fast ticking away, Exeter gave away another penalty just inside their own half, but with both Farrell and Hodgson feeling it was just out of their range, given the conditions, Hodgson kicked to the corner.
Sarries worked the ball infield from the line-out through their forwards, and with time almost up, Farrell waited in the pocket for a drop goal attempt, but a massive hit by replacement hooker Simon Alcott on Matt Stevens saw the former Bath and England prop knock-on, and another famous Exeter triumph was in the bag.
The win leaves the Chiefs in fifth place in the Premiership table, with matches against last season's top two to come in the next fortnight – away to third-place Leicester Tigers next Saturday, and at home to reigning champions and current leaders Harlequins the following weekend.
Exeter completed the league double over Leicester last season, but on both occasions the Tigers were weakened by international call-ups, and this time they will come up against the full force of the Midlanders and their huge squad.
Saracens director of rugby Mark McCall, whose side climbed to third spot despite the defeat thanks to their losing bonus point, did not have a great view of the Ashton offence but acknowledged it had been at a key time.
McCall said: "The fact that they scored a try during that sin-bin may have been our downfall.
"It was a difficult game in the conditions but their fundamentals were much better than ours.
"You can't afford to come to a place like Sandy Park and lose two men to the sin-bin.
"On top of that we gave away a number of other penalties which had consequences in the match – something that we had prided ourselves on wasn't as good."