The scores were locked at 20-20 with 12 minutes to go when the Broncos' Steve Rosolen took a pass that he will be wishing this morning had gone nowhere near him.
It was followed a fraction of a second later by the hurtling bulk of Umaga, who not only flattened him, but hit the ball so hard that it flew out to the wing and was picked up by Damian Munro.
By the time Rosolen picked himself up painfully from the turf, Monro had touched down and Halifax were in front, but the drama did not end there.
With time running out for London, it was Umaga's tackle that prevented Shaun Edwards from going under the sticks and leaving an easy conversion to win the game.
With the Halifax defence stretched, Tony Martin scored his second try of the game despite that intervention, but it was wide out and Greg Barwick could not add the goal points.
It was a match both coaches claimed they should have won, Halifax's John Pendlebury because his side was in a winning position at the death and London's Tony Currie because they had had the chances in the first half to win it twice over.
Always the more incisive and fluent side, the Broncos took an early lead and Josh White's jinking run set up Terry Matterson. Matterson, in fact, can hardly have enjoyed more freedom at any stage of his long career than he did in the first half yesterday, when he scored another try with an outrageous dummy and sent in White for a touchdown that was disallowed.
London also had another try ruled out for a marginal forward pass leaving Curry to fume: "We were by far the better side and we were brought back to Halifax's level by the official's decision. I'm sick of that happening to the London Broncos."
Halifax deserve some credit for hanging on to a contest that could already have been beyond them. Twice in the first half they drew level with close range tries from Martin Pearson and Wayne Jackson and a meagre two-point deficit at half-time inspired them to believe that they could get something out of the game after the break.
With a much tighter defensive effort putting pressure on the Broncos Halifax hit the front for the first time when Michael Jackson took an excellent pass from Karl Harrison to charge over, although Edwards' long pass enabled Russell Bawden to equalise just after the hour.
Currie will take the Broncos' complaints over John Connolly's refereeing to the League, but on reflection he might decide that it was Umaga, plus his own side's failure to take their chances, that cost them full points.
Halifax: Umaga; Tuilagi, Schuster, Amone, Munro; Pearson, Dean; Harrison, Rowley, W Jackson, M Jackson, Gillespie, Moana. Substitutes: Marshall, Chester, Highton, Rushforth.
London Broncos: Barwick; Roskell, Tollett, Krause, Smith; Edwards, White; Bawden, Beazley, Mestrov, Rosolen, Nable, Matterson. Substitutes: Dunford, Spencer, Salter, Martin.
Referee: J Connolly (Wigan).Reuse content