As a first match at Brentford's Griffin Park, it could hardly have been bettered with veterans of the club's headiest days at Craven Cottage savouring an atmosphere they have not experienced for more than a decade.
Credibility has been the buzz word for the London Broncos, both as inheritors of Fulham's mantle and prospective Super League residents. "We earned some credibility out there tonight," Gary Greinke, their coach, said.
The crowd, admittedly swelled by some free tickets, was the best since Craven Cottage despite live television, and many will be back for more after a performance that was not merely full of guts and determination but of sparkling rugby as well.
Although a line-up with three newly arrived Australians looked purposeful from the start, Leeds went 12-2 ahead with tries from Craig Innes and Jim Fallon as they briefly threatened to assert their pedigree.
But the excellent Leo Dynevor went over just before the break and London dominated the second half. Brilliant improvisation kept the ball alive after David O'Donnell's high kick, and led to Chris McKenna's try to put them in the lead. When Ikram Butt, the side's one English-born player, went over the unthinkable was firmly on the agenda.
Leeds's bad handling and failure to match London's enthusiasm had already put them in a parlous position, and indiscipline made it worse when penalties for a high tackle and for dissent allowed O'Neill to add four more points.
When Ben Walker chipped in with a drop goal and O'Neill another and a penalty in the last four minutes the Broncos were safely in the stable.
They sang "Land of Hope and Glory" before kick-off although "Advance Australia Fair" might have been more appropriate. Griffin Park might not be the promised land as the Bronco's have only one more match scheduled there this season, but after this Greinke and his men would walk across the capital to play there every week.
London Broncos: O'Neill; Butt, Cochrane, McKenna (Green, 74), Vincent; Walker, Dynevor; Mestrov, O'Donnell, D Shaw (Bawden, 74), Bryant (Bawden, 4; Bryant, 30), Rosolen, Gill (Pitt, 76).
Leeds: Cook; Fallon (Golden, 47), Hassan, Innes, Cummins; Kemp, Gibbons; Harmon (Field, 65), Lowes (Shaw, 54), Faimalo (Fozzard, 47), Morley, Mann, Forshaw.
Referee: R Smith (Castleford).Reuse content