Down inflicted a first defeat of the year on Roscommon in poor conditions at Dr Hyde Park, 0-12 to 0-7.
With the wind behind them in the first half, the visitors reeled off the first six points via Niall Donnelly, Darren O'Hagan, Ryan Johnston, Caolan Mooney and Donal O'Hare (two).
Despite having midfielder Ian Kilbride dismissed in the 15th minute for a second yellow-card offence, the Rossies landed the next three points through Cian McKeon (two) and Conor Devaney.
But the Mourne County rallied again with points from Colm Flanagan, Anthony Doherty ('45') and O'Hare to lead by 0-9 to 0-3 at the break.
The Connacht champions registered the first four points after the restart, with Diarmuid Murtagh and Donie Smith each on target twice, to set up an exciting closing quarter. It could have been even closer had not Down goalkeeper Marc Reid executed a superb save to deny half-time substitute Ciarain Murtagh from the penalty spot.
The tide seemed to have turned against them as the comeback kings gathered a head of steam but the Ulster county finished strongly with three unanswered points from O'Hagan, Darragh O'Hanlon and Niall Madine to seal their second win of the campaign and join Cork at the top of the table.
Down - M Reid; A Doherty (0-1'45), B McArdle, C Flanagan (0-1); D O'Hagan (0-1), N McParland, C Mooney (0-1); C Poland, N Donnelly (0-1); S Millar, C Maginn, R Johnston (0-1); B O'Hagan (0-1), D O'Hare (0-3, 2f), A Morgan. Subs: D McKibbin for C Poland, D O'Hanlon (0-1f) for B O'Hagan, N Madine (0-1) for D O'Hare (BC), K Quinn for B McArdle.
Roscommon - J Featherston; D Murray, J McManus, N McInerney; N Daly, F Lennon, B Stack; E Smith, I Kilbride; Finbar Cregg, N Kilroy, C Devaney (0-1); D Murtagh (0-2f), C Lennon, C McKeon (0-2f). Subs: C Murtagh for Finbar Cregg, D Smith (0-2, 1'45) for C McKeon, C Daly for F Lennon, H Darcy for N Kilroy, S McDermott for B Stack, U Harney for E Smith.
Referee - S Hurson.