The Broncos' three-match unbeaten run came to an abrupt end at Langtree Park with St Helens running in six tries without reply.
A rash of penalties made the game a stop-start affair with the Broncos unable to break down a solid St Helens defence.
Head coach Tony Rea said: "The scoreline reflected the night, it wasn't good enough from us as a group. We didn’t play as a team for long enough periods. You get highs and lows in games like that and we were too low at times
"We lost each other out there and played like a collection of individuals at times and it was reflected in the fact that we couldn't find any points."
St Helens opened the scoring after three minutes following successive penalties conceded by the Broncos. After several drives to the line, James Roby fired a bullet pass to Tony Puletua who crashed over by the posts.
Jonny Lomax converted but from Kieran Dixon's re-start Puletua knocked on behind his own line to give the Broncos their first good attacking position but they weren't able to turn it into points. As the half wore on the Londoners had their chances, particularly when they were given three successive penalties 15 metres from the St Helens line.
Once again they weren't able to turn that pressure into points but they were defending well . The game was being dominated by the whistle of referee Silverwood but a scintillating 50 metre run by Dixon down the middle of the field from his own 20 metre line brought generous applause from the home fans.
The game lacked any continuity due to the high penalty count but just before half time yet another penalty enabled Saints to move up field and a dart by Lomax was finished off by Mark Flanagan to make it 10-0 at the interval.
Five minutes into the second half St Helens went further ahead when the Broncos defence failed to deal with what looked like an innocuous grubber kick to the line from Lomax. Flanagan managed to touch it down for his second try to make it 14-0.
Minutes later a knock on by the Broncos just 15 metres from their own line presented the home side with another scoring opportunity, Paul Wellens racing through and forcing his way over the line. The one consolation for the Broncos was the inability by Lomax to convert those last three tries.
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The score seemed to galvanise the visitors and they forced successive goal line drop out followed by a penalty which gave them four consecutive sets of tackles but they still weren't able to crack a solid Saints defence.
Having weathered the storm, St Helens came roaring back, Wellens grabbing his second touchdown and Gary Wheeler converting to make it 24-0 going into the final quarter. As the game drifted towards its inevitable conclusion, Anthony Lanfranchi wrapped things up with a try in the final minute which Wheeler converted.
Broncos: Robertson, Dixon, O'Callaghan, Howell, Caro, Dorn, Gower, Kaufusi, Randall, Wheeldon, Lovell, Clubb, Bolger Interchange: Rinaldi, Bryant, Krasniqi, McMeeken
