Monaghan 2-12 Dublin 0-17
Monaghan beat Dublin for the first time since 2006 with a one-point win in front of 22,085 spectators at Croke Park.
It is only the Dubs' second league or Championship defeat since the start of 2015.
In what was a dead rubber clash, with Dublin already through to next weekend's Division 1 League decider, a dramatic last-gasp point from Fintan Kelly in the third minute of injury-time earned the Ulster side victory.
Earlier, a 65th-minute goal from substitute Jack McCarron helped to turn this game in the Farney County's favour.
McCarron's three-pointer helped Monaghan to a 2-10 to 0-15 lead, and although the sides were twice level after this - it helped Monaghan grow in confidence.
In truth, little separated the counties throughout this contest, and they were twice level inside the opening four minutes.
Vinny Corey and Dean Rock trading points, before Conor McManus and Rock swapped scores.
Dublin pushed three points clear following efforts from Brian Fenton, Rock and Philly McMahon.
Monaghan offered a strong response with Dessie Mone cutting the gap, before a 12th minute Corey goal handed them the lead once more.
John Small and Rock pushed Dublin ahead, but the sides were level again after 22 minutes following a Conor McCarthy pointed free.
From then until the break scores were at a premium, with just a point each, with Brian Howard edging Dublin ahead before a 29th minute McCarthy free ensured the sides were tied 1-5 to 0-8 at the interval.
It was far from a classic game, but it continued to prove tight on the restart.
McCarthy continued to pick off some fine points for Monaghan and he pushed them back ahead early on the resumption.
Once again Rock levelled before McMahon registered his second point of the day.
Dublin introduced Colm Basquel and Michael Daragh Macauley for Kevin McManamon and Shane Carthy.
Kieran Hughes and Niall Scully traded points before another Rock point handed Dublin a 0-12 to 1-7 lead after 47 minutes.
Ryan McAnespie cut the gap to a point before substitute Basquel restored Dublin's two-point lead.
Another Rock free, after good work by Michael Fitzsimons ensured a 0-14 to 1-9 lead with 10 minutes remaining, but Monaghan upped their game.
Karl O'Connell took a fine point, before Jack McCarron's goal ensured a grandstand finish.
Brian Howard levelled in the first minute of injury-time, but there was still time for Kelly to snatch a winner.
MONAGHAN: R Beggan; C Boyle, D Wylie, R Wylie; D Mone (0-1), V Corey (1-1), K O'Connell (0-1); D Hughes, N Kearns; P McKenna, O Duffy, R McAnespie (0-1); C McCarthy (0-3, 2f), K Hughes (0-1), C McManus (0-1). Subs: F Kelly (0-1) for McKenna (47), D Ward for Duffy (47), C Walshe for Mone (BC 56), J McCarron (1-1) for McCarthy (56), N McAdam for Kearns (59), T Kerr for K Hughes (71).
DUBLIN: E Comerford; M Fitzsimons, P McMahon (0-2), D Byrne (0-1); D Daly, J Small (0-1), B Howard (0-2); J McCarthy, B Fenton (0-2); S Carthy (St Vincent's), C Costello, N Scully (0-1); C McHugh, D Rock (0-7, 4f), K McManamon. Subs: C Basquel (0-1) for McManamon (44), MD Macauley for Carthy (44), E Murchin for Daly (54), P Small for McHugh (54), E Ó Conghaile for Costello (64).
REFEREE: David Gough (Meath).