Finn's scoring leads Exiles' recovery
London recovered from a shambolic start against Mayo, where they conceded two goals in the opening two minutes, to lead by 2-10 to 2-3 at the break.
Two early Kenny Feeney frees set the tone for the second half, and Mayo were given hope when London 'keeper Tommy Williams spilled Keith Higgins' tame effort into the path of the grateful Cathal Freeman.
However, indiscipline and a goalkeeping error gave Mayo further hope, and London were lucky to see a Donal O'Brien free whizz inches over the bar deep in injury time.
"The lads showed great character," said Exiles manager Eamonn Phelan.
"Two goals down after two minutes, to come back and lead by seven points at half-time was a big turnaround."
Man of the Match: Martin Finn (London)
Scorers -- London: M Finn 1-9 (5f), J Maher 1-2, J Egan 0-2, S Ryan, H Vaughan 0-1 each.
Mayo: B Hunt 2-0, C Freeman 1-0, K Feeney 0-5 (5f), D McDonnell, K Higgins (1f) 0-2 each, D O'Brien 0-1.
London -- T Williams; E Walsh, B Costello, G Fennelly; M Walsh, PJ Rowe, L Mackey; C Quinn, D Maher; S Ryan, J Egan, H Vaughan; J Maher, M Finn, K Walsh. Subs: T Hogan for Mackey (32), P Sloane for Ryan (41), S Egan for J Egan (55), R Darcy for Vaughan (63), E Gleeson for J Maher (66).
Mayo -- D O'Brien; S Morley, A Connolly, A Brennan; P O'Flynn, P Connell, S Connell; C Freeman, D McConn; D McDonnell, K Higgins, P O'Grady; D McTighe, K Feeney, B Hunt. Subs: S Markham for O'Grady (32), G Henry for McTighe (63).
Ref -- D Hughes (Carlow)