Leitrim and London will have to meet again for a spot in the Connacht SFC final after a pulsating 2-07 to 0-13 draw in Carrick-on-Shannon.
Goals in each half from Lorcan Mulvey and substitute Sean Kelly looked to have sealed the win for the Exiles, but Darren Sweeney and Kevin Conlon kicked late points to seal a draw for Leitrim.
Leitrim's challenge received a huge blow when star forward Emlyn Mulligan limped off after 15 minutes, but they looked like reaching the Connacht final after a great start to the second half saw them pull two points clear.
But they must meet again after a breathtaking finish at Pairc Sean Mac Diarmada.
Indeed Leitrim had the chance to snatch an undeserved victory with a 45 with the last kick of the game, but with his first effort of the game full-back Ciaran Egan screwed his effort wide as a share of the spoils resulted.
London impressed with an intense start and after Paddy McGowan gave the home side the lead, Seamus Hannon levelled matters with a great point after a driving run.
One of Leitrim's outstanding performers, Darren Sweeney, pointed in the fourth minute, but the Exiles hit a good spell with a Padraig McGoldrick free and Mulvey point to give them the lead.
But with Mulligan departing with a calf injury Leitrim upped their intensity and hit four of the next five points to take a 0-6 to 0-4 lead by the 23rd minute.
Two of those points arrived from primary possession gained around the middle of the field as the home side began to stamp out London's early ascendancy in that area.
But just before the break Mulvey finished to the net from a yard out after Cathal McCrann failed to hold on to a high punt into the square from Cathal Magee, which gave the visitors a 1-4 to 0-6 lead at half-time.
That goal stunned the home side, but Leitrim recovered well after the break with four well worked points, while a 45 from Declan Traynor was the sole reply for the Exiles.
However, they looked certain winners when Kelly hooked the ball past McCrann 11 minutes from time, only for Leitrim to clinch the draw with Conlon's late point.
Leitrim: C McCrann; A Wynne, C Egan, G Reynolds; D Beck, E Williams, B Prior; D Sweeney (0-02), B Brennan (0-02), P McGowan (0-02), E Mulligan (0-01, 0-01f), P Brennan (0-01); R Lowe (0-01), J Glancy (0-01), K Conlon (0-03, 0-02f).
Subs: C Reynolds for Mulligan (15 mins), A Croal for Reynolds (55 mins), S McWeeney for Beck (67 mins), R Cox for Conlon (72 mins).
London: D Traynor (0-01, 0-01'45); P Butler, S Curran, D McGreevy; S Hannon (0-01), S Mulligan, T Gaughan; M Gottsche (0-01, 0-01f), C Doyle; G Crowley, C McCallion, B Mitchell; P McGoldrick (0-01, 0-01f), L Mulvey (1-01), C Magee (0-01).
Subs: P Geraghty for Gottsche (29 mins), D Dunleavy for Mitchell (38 mins), E O'Neill for McGoldrick (53 mins), S Kelly (1-01) for Doyle (53 mins), D O'Neill for McCallion (69 mins).
Referee: Barry Cassidy (Derry).