Joe Brolly laid into Donegal after Robert Hennelly's last-gasp equaliser secured a point for Mayo at Markievicz Park.
Despite being down to 14 men after Stephen Coen's sending off, James Horan's men rattled off the last four points of the game to dig out a result in dramatic fashion.
Hennelly was the hero of the hour with a penalty save from Paddy McBrearty's second half spot-kick and a nerveless late equaliser from a free in wet, windy conditions.
