Sean McCormack landed a splendid long-range free-kick deep in stoppage time to earn Longford a draw at Pearse Park.
The Rossies held a three-point cushion at the interval in this local derby, but the home side quickly bridged the deficit with scores from McCormack and David Barden, who was making a welcome return to inter-county football.
Roscommon dominated the early exchanges and looked a lot sharper in front of the target. Free-taker John Rogers took full advantage of Longford's lack of discipline and he raised the white flag three times in the first half.
Twenty minutes had elapsed before Glenn Ryan's men finally registered their opening point from play. Paul Barden instigated the move after he played the ball into the path of McCormack and the nippy corner-forward duly slotted over from an acute angle.
After the break, Longford continued to trim the margin back but the loss of centre-back Enda Williams and goalkeeper Damien Sheridan, who both picked up serious injuries, weakened their position.
A glorious Paul Barden goal into the top corner put Longford ahead for the first time in the 48th minute. This brief lead was cancelled out over the following 15 minutes with the visitors regaining control with points from sub Cathal Shine and Rogers.
A Ger Heneghan point appeared to have snatched the win for Roscommon with five minutes remaining, but McCormack rescued a point for the hosts with a fantastic dead-ball effort in stoppage time.
Scorers -- Longford: S McCormack 0-5 (3f), P Barden 1-0, B McElvaney (f), D Barden 0-1 each. Roscommon: J Rogers 0-4f, G Heneghan 0-2, S Ormsby, N Carty, K Higgins, C Shine 0-1 each.
Longford -- D Sheridan; D Brady, B Gilleran, D Reilly; S Mulligan, E Williams, P Foy; K Diffley, B McElvaney; P Barden, D McElligott, D Barden; Noel Farrell, P Dowd, S McCormack. Subs: M Brady for E Williams (inj, h-t), J McKenna for D Sheridan (inj, 43), Niall Mulligan for N Farrell (51).
Roscommon -- M Miley; S McDermott, D Ward, S Ormsby; N Carty, D Keenan, S Percell; M Finneran, K Higgins; D O'Gara, C Devanney, C Cregg; J Rogers, P Garvey, G Heneghan. Subs: C Shine for P Garvey (52), F Cregg for D O'Gara (73).
Ref -- J Henry (Mayo).