A week away from the Challenge Cup final at Wembley, coach Tony Smith chose to rest a swathe of Warrington stars, including Lee Briers, Garreth Carvell, Ben Harrison, Brett Hodgson, Joel Monaghan and Ben Westwood.
And their deputies had no answers to an opportunist London side, who ran in 10 unanswered tries in the second half to rack up a cricket score.
Luke Dorn, four, Michael Robertson, two, Kieran Dixon, Will Lovell, Omari Caro and Julien Rinaldi all crossed for the Broncos, while Craig Gower kicked nine goals.
In the night's other Super League game, St Helens beat Castleford 44-12 at Langtree Park.
Tommy Makinson was the standout performer for Saints with a 12-point haul, with Anthony Laffranchi, Paul Wellens and Chris Flannery also going over in the first half.
After the break, Saints ran in a further four tries, courtesy of Makinson again, Gary Wheeler, Adam Swift and Jonny Lomax.
Castleford's responses came from Paul Jackson in the first half and Steve Snitch in the second.
- Joel Monaghan
- Garreth Carvell
- Brett Hodgson
- Lee Briers
- Julien Rinaldi