Two goals by second-half substitute Ronan Kennedy gave Leitrim victory over London but Brendan Guckian’s team were made to work very hard before triumphing at the redeveloped Ruislip.
His side now advance to a Connacht semi-final against Roscommon on 18 June at Dr Hyde Park while London enter the qualifiers.
A 2-01 scoring glut by the Ridge County in six second-half minutes settled the contest.
Keith Beirne’s free was followed by Kennedy’s two goals in the 51st and 54th minutes.
Rory Mason’s 46th-minute effort had given London a two-point lead and Mason went close to scoring a goal when his pointed effort struck Brendan Flynn’s upright minutes before Kennedy’s first goal.
The Maothail clubman executed two lethal finishes into the top corner past Gavin McEvoy after finding space to shoot from close distance.
Exiles captain Liam Gavaghan produced a heroic performance at centre-half forward and later full-forward, scoring a total of eight points.
Former Tyrone All-Star Owen Mulligan was a late inclusion at corner-forward for Ciaran Deely’s side and the three-time All-Ireland winner scored a fine point in the 43rd minute to level the tie, 0-09 to 1-06.
A Darragh Rooney goal midway through the first half gave Leitrim a five-point lead after the sides were level pegging throughout the early stages.
Gavaghan had previously scored a brace of points in reply to scoring efforts from Rooney and Leitrim midfielder Damien Moran, who shot three fine points from distance in the opening period.
Keith Beirne was on free-taking duties for the injured Emlyn Mulligan and the corner-forward had a difficult first half from placed balls, kicking three wides before converting his first score on 31 minutes.
London responded through a Gavaghan score and full-forward Conor Doran’s long distance point after good build-up play reduced Leitrim’s lead 1-06 to 0-07 at the interval.
London carried their momentum into the second half with Mason, Mulliigan and Gavaghan all scoring without reply before Kennedy’s two goals re-established control for Leitrim.
London refused to go quietly and kept in touch with two points from Gavaghan and another from Mason to make it 3-08 to 0-15 with six minutes remaining.
The Exiles pushed for that elusive goal as Leitrim packed their defence clinging to their slender lead but a late Beirne ’45 and a composed score from substitute Gary Plunkett in stoppage time ended a spirited London fightback.
London: G.McEvoy, P. Butler, C. Coyne, C. O'Neill M. Jordan, R. Jones, C. Dunne, A McDermott, L. Gavaghan (0-8, 0-02 frees ), M. Carroll, M. Gottsche ( 0-1 45’ ), J. Branagan, R. Mason (0-04, 0-03 frees), Doran ( 0-2), O. Mulligan (0-01)
Subs: G. Crowley for O’Carroll (50), K. Hughes for Doran (54), D. Carrabine for Dunne 58’, C. Dunne for Jordan (65)
Leitrim: B. Flynn, M. McWeeney, R. Gallagher, P.Maguire, J. Rooney, D. Wrynn, O. Madden, S. Moran, D. Moran (0-3),D. McGovern ( 0-1 ), B. Gallagher, R.O'Rourke, K. Beirne (0-03, 0-02 frees 0-01 45’), C. Gaffney, D. Rooney (1-2)
Subs: R. Kennedy (2-0) for Gaffney (40), W. McKeon for Gallagher (46), G. Plunckett (0-01) for Moran (53), N.Plunkett for Madden (55), C. Cullen for Moran (65)
Referee: Noel Mooney (Cavan)