The Broncos lost their opening league game at home to Halifax last week and they then saw their coach, Tony Currie, return to Australia because of a family illness.
Hull only lead 2-0 at half-time despite playing with a stiff wind behind them and London went ahead on 59 minutes. Damien Chapman burst through the defence and exchanged passes with Nick Mardon before crashing over but the scrum-half missed the relatively simple conversion.
Hull turned down two chances to kick at goal from close range in the dying minutes as they attempted to claim the victory rather than settle for a draw.
They then ran the ball on the last tackle and Hitro Okesene, Alan Hunte and Graeme Hallas - who had kicked his side into the lead with a first half penalty - combined to set up Johnson and the South African winger dived over in the corner.
A superb first-half show put Salford Reds on their way to their first win of the season in the JJB Super League at Wilderspool yesterday. Salford romped into a 22-4 interval lead against an outclassed Warrington side, eventually winning 37-4.
Darryl Van de Velde, the Warrington coach, said: "It was a very poor performance and we can have no excuses. There was little enthusiasm from our side."Reuse content