The handling skills of Jamie Lyon were pivotal as Saints climbed above Leeds with what could be, three rounds from the end of the regular season, perfect timing.
Saints took just five minutes to go into the lead, with the help of a ball lost in the tackle by Mark Tookey, who was only in the London starting line-up because Steve Trindall had been taken ill before the match. Lyon produced one of his trademark back-handed passes and his fellow Australian Darren Albert, as so often, made the most of it, beating the two remaining defenders for opening try.
Keiron Cunningham's surge from dummy-half and link with Paul Wellens created a second Saints try, for Jason Hooper. A prolonged period of pressure brought no joy for London and it took a good tackle by their new loan signing from Leeds, Carl Ablett, to snuff the chance of Albert scoring his second from the wing.
At the other end, a long chase by Ade Gardner prevented Luke Dorn from striking back for the Broncos. It was their most dangerous moment, because much of their other more promising work was ruined by erratic handling and some strange tactical options.
Saints were not exactly playing like league leaders themselves, but they know how to take their chances and that is what they did five minutes before half-time when Lyon and Albert again opened up the left flank of the London defence and Sean Long took Lyon's inside pass to score.
Saints carried on after the break with Long and James Graham setting up Lee Gilmour and almost immediately Zeb Luisi dropped Long's high kick, Lyon picked up and Paul Anderson romped over.
They were really in their stride by now and the crispest, flattest of passes from Cunningham sent John Wilkin racing away.
It was already far too late for London, long before Nick Bradley-Qualilawa scored their only try from Tyrone Smith's pass.
The imperious Lyon released Albert for his second try shortly after that, closely followed by Cunningham going over from close range and another one from Paul Wellens.
On this showing, London will find it very difficult to hang on to sixth place ahead of Wigan and Huddersfield. The only bad news for Saints came in the form of injuries to Mark Edmondson and Vinnie Anderson.
St Helens: Wellens; Albert, Lyon, Talau, Gardner; Hooper, Long; Fozzard, Cunningham, P Anderson, Wilkin, Gilmour, V Anderson. Substitutes used: Edmondson, Fa'savalu, Roby, Graham.
London Broncos: Luisi; Wells, Smith, Sykes, Bradley-Qalilawa; McLinden, Dorn; Tookey, Hopkins, Armour, Houmono, Mateo, Mbu. Substitutes used: Williams, Stephenson, Lolohea, Ablett.
Referee: G Black (New Zealand).Reuse content