WGC lost in the league for only the second time this season and this was a first defeat away from Herns Lane, as they gave a very mediocre performance in their much postponed trip to Southall.
The hosts, who have been inactive for a great deal of the early part of this year due to an unfit ground, started very brightly and tested the WGC defence with long balls to their pacy wingers.
It was a tactic that brought dividends as early as the ninth minute, when striker Edison Teberen broke clear of Jay Lovell's attentions to run in unchallenged and slotted the opener past WGC keeper Joe Croft.
It took WGC just two minutes to level, Sean Brettell's cross finding Marc Arnott in the box and he turned neatly and croedded to the far post where Jason Caswell was on hand to side-foot in his 15th of the season.
Matters remained fairly even until four minutes from the break, when Teberen restored his side's lead, lobbing Croft from way out, the WGC keeper being stranded on his 18 yard line, as the effort dropped in behind him.
In stoppage time at the end of the half, Southall made it 3-1, when another through ball caught out the WGC defence and Isaac Asare rounded Croft to roll in the Southall third.
WGC's woeful night continued four minutes after the restart, when Daryl Smith was very harshly adjudged to have brought down a home forward, with what looked like a perfectly timed tackle and a penalty was awarded.
Teberen stepped up and scored, but the referee ordered a re-take for encroachment and booked Craig Arnott in the process. Croft guessed right from the re-take and made a superb one-handed save to turn the ball around the post and keep the deficit to two.
WGC were stirred into something like their usual form at this point and began to dominate possession, without really threatening to cut the deficit.
Then with nine minutes remaining, Marc Arnott broke down the left and crossed and Daryl Smith was on hand to side-foot in WGC's second, with the home defence looking for an offside flag that never came.
Croft had to be alert as Southall responded, racing from his line to block an Asare attempt, while Caswell had a late opportunity to bring the scores level, but headed straight at the keeper in the game's final minute.
Southall celebrated like it was a cup final win at the final whistle, having taken the league leaders' scalp, while this display only serves to emphasise to WGC that this division is far from won.
WGC: Croft, Perrin, Kenna, Dekanski, Lovell (Arnott C 45), Arnott (M), Smith, Boodhoo (Cifuentes 45), Brettell, Caswell, Norris (James 72).