Former Leicester forward Thomas Waldrom scored twice as Exeter Chiefs conquered Franklin’s Gardens under the Friday night lights.
Table-topping Saints were left stunned as the Chiefs claimed three first-half tries on their way to a 24-18 Aviva Premiership success.
Scores from lively duo Tom Stephenson and Jamie Elliott threatened to inspire a comeback, but Jim Mallinder’s men were forced to endure their second league defeat of the season.
Exeter laid the foundations with a stirring first 40 minutes, which began with a Luke Cowan-Dickie score and ended with Waldrom dotting down from a huge scrum shove.
In between times, the No.8 had intercepted a Stephen Myler pass and charged from halfway to reach the line.
Myler had replied with two penalties and although Stephenson and Elliott did their best to engineer a comeback, Saints had to make do with a losing bonus point.
Exeter had looked dangerous from the off, and Saints were to get off to the worst possible start.
Tom Collins’ bravery on his own line halted Jack Nowell, but it only provided a brief reprieve as hooker Cowan-Dickie scored from a lineout drive.
Fly-half Gareth Steenson’s conversion was a confident one, mirroring the start made by his team, who were 7-0 up and saw Saints forced to withdraw injured wing Collins.
After a slow start, the home team were eager for an immediate riposte, and Myler’s penalty provided it.
And he was on target again soon after as Saints started to turn up the heat, with Samu Manoa particularly prominent in the opening stages.
Exeter, to their credit, were leaving few gaps though, suffocating their opponents.
It was the sort of encounter the Chuckle Brothers would be relish, with lots of to-me, to-you as both sides used the boot to try to gain territorial advantage.
A Luther Burrell burst did provide a spark, but his attempt to chip the final defender did not pay off.
Saints were making all the running, but were becoming increasingly frustrated, and their impatience was to cost them 10 minutes before the break.
Myler’s pass was intercepted by Waldrom on halfway and the sizeable No.8 charged towards the line before performing a power slide to dot down.
Steenson’s conversion handed the Chiefs an eight-point cushion, before Manoa and Lee Dickson threatened to help Saints respond.
The American forward smashed his way clear and handed the ball to Dickson, but the final pass was too low for Mike Haywood, who knocked on with the line in sight.
And Exeter were to punish the home side’s profligacy in ruthless fashion.
After the TMO deemed the Chiefs had been held up, the visiting pack got a shove on in the five-metre scrum and Waldrom picked up to score.
Steenson’s conversion put the Chiefs into a commanding 21-6 half-time lead, leaving Saints with a huge task on their hands in the second half.
The home faithful did their best to rally their troops, but the away side were still looking sharp with the ball in hand.
And they certainly had the upper hand in the forward battle, with Saints continually frustrated up front.
One lineout drive was roared towards the line, but Exeter defended strongly, winning a scrum to prompt wild celebrations in the visiting pack.
The Chiefs forwards were enjoying their night’s work and after yet another penalty was won, Steenson increased the lead.
Saints needed some light at the end of the tunnel, something to lift the spirits on a tough evening.
The razor-sharp Stephenson was the man to provide it, latching on to an inside pass and flying over the line to a backdrop of relieved roars.
Myler made the conversion and Exeter’s lead was cut to 11 with 20 minutes to play.
Suddenly, Saints had the bit between their teeth, pouring forward and eventually forcing Exeter to crack as Elliott scored in the corner.
But Myler missed the conversion and Exeter refused to buckle again, celebrating vociferously as the final whistle signalled a famous win.
Saints: Foden; Elliott, Stephenson, Burrell, Collins (Wilson 3); Myler, Dickson; A Waller (E Waller 61), Haywood, Ma’afu (Denman 54); Manoa, Day; Clark, Nutley (Harrison 61), Dowson (c).
Replacements not used: McMillan, Woolford, Hodgson, Waldouck.
Exeter: Dollman (Whitten 60); Nowell, Slade, Hill, Jess; Steenson (McGuigan 70), Chudley; Rimmer, Cowan-Dickie (Bateman 70), Francis (Low 57); Mumm (c), Welch (Caldwell 67); White (Horstmann 60), Armand, Waldrom.
Replacements: Moon, Thomas.
Referee: Dean Richards