Electrifying displays from goalscorers Jermaine Beckford and Cleveland Taylor fired Scunthorpe to their first win over the Bees in 30 years, but only after Brentford captain Kevin O'Connor squandered an early penalty that the relegation-threatened side could ill afford to miss.
While victory leaves Scunthorpe in seventh heaven, the relegation trapdoor yawns ever wider for Brentford.
A match that kicked off in brilliant sunshine should have started equally brightly for Brentford, but Fitzgerald's side squandered two gilt-edged early opportunities to open the scoring.
The first came when Calum Willock found Paul Brooker in space ten yards out only for the midfielder to blast wastefully wide. But Brooker's profligacy was nothing compared to O'Connor's 12th minute penalty miss.
Normally the Bees' most reliable performer, the set-piece specialist stepped up confidently after Neil Shipperley had been brought down in the box by Billy Sharp only to blast his spot-kick out of the ground.
Scunthorpe had threatened sporadically up to that point with Sharp and Beckford the predictable mischief makers, but the narrow escape was enough to spark the visitors' attacking machinery into overdrive.
Beckford rattled the woodwork with a curling shot from the edge of the area before Richard Hinds repeated the feat with a close-range header.
Brentford were living on borrowed time and the breakthrough duly arrived five minutes before the interval.
A defensive error by Andy Frampton let in Beckford and the skilful striker needed no second invitation as he fired the ball low and true across Nathan Abbey for his fourth goal in five games.
The second half followed a similar pattern with Brentford threatening early on through Brooker, Shipperley and Charlie Ide only for the visitors to hit back with a series of devastatingly quick counter-attacks.
The most telling of these came with a minute to go when Sharp fed the outstanding Taylor, who slotted home to seal the points for Scunthorpe.