WGC boss Adam Fisher suffered a run of three successive defeats for the first time in his managerial career, when the Citizens lost this closely fought, midweek clash at Stanstead Abbotts by a single goal.
Unlike the previous two reversals at home to Broxbourne and at Holmer Green - games that produced seven and eight goals respectively - this was a tight affair, but WGC still came out on the wrong end of it.
Certainly, the home Saints didn't look a side in the bottom three of the SSML Premier in the way that they battled WGC, who were sitting fifth top before this game.
WGC welcomed back Carl Mensah (foot) after injury and Ashley Kersey, following suspension, to their line-up and the pair did strength the visitors', particularly in the opening hour.
New keeper Grant Beckwith was in action in seven minutes saving with his legs, from the home side's lively striker Kieran Smith.
But after an opening quarter largely played in midfield, it was Kersey who had WGC's first chance on 20 minutes, losing his marker from a Jay Lovell cross, only to head powerfully off target.
As the game opened up, WGC had a real let-off when keeper Beckwith scuffed a clearance straight to the Saints' winger Roel Harper, who reprieved both the keeper and the visitors by screwing his shot wide of an open goal.
Kersey again beat the Bury defence in the air to win another header, but again his final effort missed the target.
The home side had ex-Hatfield keeper Allan Buck between their posts and the big keeper always reserves a good performance for meeting WGC. He pulled off a fine save to thwart Jason Caswell, after Kersey had again done well to retrieve Lovell's overhit cross.
There was another let-off for WGC on the half-hour when Harper reached a cross before keeper Beckwith and shot over him. For the second, successive
game, the keeper was able to snatch up a rebound off the woodwork, to keep the game goalless.
Aaron Cato, restored to WGC starting line-up, was playing impressively and he hit the best effort of the half - a stinging drive towards the top corner - only to see Buck pull off another outstanding save, tipping it away.
The second-half began with Beckwith making a sharp save on his far post from Kieran Smith's header from a left-wing cross.
Then on 58 minutes, St Mags broke the deadlock, capitalising on a catalogue of WGC mistakes.
Firstly, Juan Cifuentes failed to put in a challenge on half-way, then Mensah went in and missed a tackle, allowing Harper to race clear of the visiting defence. Beckwith came racing out of goal, but was easily avoided, as Harper side-stepped around him and rolled the winner into an empty net from 20 yards.
Manager Fisher immediately introduced Craig Arnott and Dave Parkinson for Kersey and Cato, who hadn't been as effective as in the first 45 minutes and then send on Reggie Ross for the final quarter.
But none of the trio had any impact, other than Parkinson receiving a red card three minutes from time, for kicking out in frustration at an opponent, after being fouled challenging for an aerial ball.
Buck continued his impressive showing late on, as he made another outstanding block to further deny Caswell, as WGC battled in vain for an elusive equaliser.
WGC: Beckwith, Lovell, Mensah, Boodhoo, Welsh, Cifuentes, Dimmock, Cato (Parkinson 63), Bronti (Ross 77), Caswell, Kersey (Arnott 63).