Antrim negotiated a tricky trip to Ruislip with substitute Kevin Niblock scoring a crucial second-half goal to secure a 2-11 to 2-09 win.
London looked on course for a shock All-Ireland Senior Football Championship qualifier first round victory as goals from Ciaran McCallion and Eoin O’Neill - the second on the stroke of half-time - moved them 2-05 to 1-05 ahead.
The Exiles were let down by nine wides before the break and, with the wind behind them, Antrim swept through thanks to Niblock’s 64th-minute strike and a late Tomás McCann point.
With just two previous Senior Championship wins under their belt, London were always going to be up against it.
However, a slender loss to Leitrim last time out meant hopes were high in the Exiles camp that they could claim a win this time around.
Antrim's preparations were less than ideal with the bulk of their squad flying over this morning. Most of their players had attended the wedding of forward Tomas McCann yesterday afternoon.
McCann though led by example, with the 24-year-old corner forward in top-scoring form. He finished with 0-05 over the course of the 70 minutes.
While Antrim came good when it mattered most, it was the hosts who started brightly. Good work between defence and attack gave Paul Coggins' charges the opening score of the game.
Full-forward Eoin O'Neill registering his lone score of the day after London captain and Antrim native Sean McVeigh had put in some solid work at the back.
London's lead was shortlived however as Antrim got motoring to register 1-03 without reply and take a five-point lead by the end of the first quarter.
McCann sent over his first point to tie the game before efforts from defender James Loughrey and Conor Murray ensured a 0-03 to 0-01 advantage.
Goal chances suddenly came from all angles for Antrim, but Aodhan Gallagher squandered a close range chance in front of the posts before the St Gall's midfielder made amends in the 18th minute.
Gallagher fired ball past London goalkeeper Evan Byrne after McCann had delivered the final pass. The Saffrons' goal seemed to kickstart a London rival as the hosts hit back strongly.
London carved into the Antrim lead with points from Sean Kelly and John Scanlon, cutting the gap to a goal approaching the break.
Goggins' side had the majority of possession at this stage, but also squandered some gilt-edged chances in front of the posts. Kevin O'Leary and Anthony Gaughan both struck wides before McCallion netted.
McVeigh, who pushed forward on a number of occasions, combinined well with McCallion to tee up the goal which made it 1-03 apiece.
Antrim briefly took the lead thanks to a Mark Sweeney score, but London were strongest before the break. Michael Mullins and McVeigh picked off points before Eoin O'Neill broke through for London's second goal.
He was alert to a quickly-taken free and managed to beat Antrim stopper Chris Kerr with a rasping shot from 21 metres out. That was the last action of the opening half as London went in a goal clear.
Antrim fought back on the restart to level the contest six minutes into the second half, thanks to points from Conal Kelly, Conor Murray and McCann.
London then edged ahead again thanks to a second McVeigh score, but the Exiles were struggling to get to grips with an Antrim side who had seized control of the midfield sector.
McCann and James Loughrey tagged on scores to push Antrim two points clear in the 48th minute, but London failed to give up.
Lorcan Mulvey was industrious around centre-field, while Mark Gottsche continued to play more of an attacking role. This paid off with Gottsche cutting the gap to the minimum before points from McCallion and Gottsche again gave London a two-point cushion with nine minutes left on the clock.
However, Niblock's goal soon after gave the Ulster men a bit of breathing space and although London controlled most of the possession in the final stages, they were unable to get the scores required against a dogged Antrim defence.
There were missed opportunities for McCallion, Gottsche and McVeigh as London endured a frustrating finish to their 2012 Championship campaign.
Scorers - London: C McCallion, E O'Neill 1-01 each, S McVeigh, M Gottsche (0-01f) 0-02 each, S Kelly (0-01f), M Mullins, J Scanlon 0-01 each
Antrim: T McCann 0-05 (0-04f), K Niblock, A Gallagher 1-00 each, J Loughrey, C Murray 0-02 each, M Sweeney, C Kelly 0-01 each
LONDON: E Byrne; J Scanlon, S McVeigh, D McGreevy; A Gaughan, S Mulligan, S Hannon; L Mulvey, M Gottsche; S Kelly, K O'Leary, M Mullins; C McCallion, E O'Neill, G Crowley.
Subs used: P McGoldrick for Kelly (41 mins), B Osbourne for McGreevy (46), P Finn for Crowley (53), M Carroll for Mullins (64), N Egan for O'Neill (67).
ANTRIM: C Kerr; A Healy, R Johnson, K O'Boyle; T Scullion, J Crozier, J Loughrey; M McCann, A Gallagher; C Murray, M Sweeney, C Kelly; T McCann, M Magill, M Johnston.
Subs used: D O'Hagan for Healy (61 mins), M Armstrong for Murray (69).
Referee: Padraig Hughes (Armagh)