Mayo started the day hoping to build on ambitions to take a step towards a possible Allianz League final place next month and ended it very close to the Division 1 relegation zone.
Meanwhile, Cavan have given themselves a chance of escaping the relation trap door, which seemed set to snap down on them after taking only one of a possible eight points.
Their first first win was achieved with real determination as they came from five points down late in the first half to edge past Mayo in a tight, tense second half.
Gerard McKiernan scored 1-5 in a great Cavan victory which was fashioned on a massed defence when Mayo had possession and quick breakouts when the chances arose.
Mayo were hot favourites to win on home ground in MacHale Park but misfired badly in the second half as gritty Cavan took them on with power and pace.
Mayo led by 0-9 to 1-5 at half-time, having had a five point cut to one just before the whistle when McKiernan struck for 1-1 from open play to add to the two points he had kicked earlier.
The goal, expertly finished after the midfielder drifted in close to the Mayo goal, was the last action of a half where Mayo were generally the tidier performers,
Andy Moran, Conor O’Shea and midfielder Danny Kirby each kicked two points as patient build-ups against a massed Cavan defence yielded dividends.
Cavan had some good chances too but were let down by inaccurate shooting, especially in the opening quarter when they shot six wides, a figure that had increased to eight by half-time.
Cavan started the second half very well and led by 1-9 to 0-10 after 45 minutes before Mayo fought back. They were ahead after 58 minutes but three points by McKiernan, Dara McVeety and sub John McCutcheon gave Cavan a crucial win.
Cavan: G McKiernan 1-5 (3f), D McVeety 0-3, T Corr 0-2, R Dunne, C Madden, M Reilly, J McCutcheon 0-1 each.
Scorers: D Kirby 0-4, A Moran 0-3, L Keegan, C O’Shea 0-2 each, T Parsons, F Boland, K McLoughlin (f), S Nally 0-1 each.
Mayo: D Clarke; B Harrison, K Higgins, P Durcan; C Boyle, L Keegan, D Vaughan; T Parsons, D Kirby; F Boland, C O’Connor, C O’Shea; K McLoughlin, A Moran, C Loftus.
Subs: S Coen for Vaughan (53), S Nally for Boland (55), E Regan for Loftus (61), N Douglas for O’Shea (66).
Cavan: R Galligan: F Reilly, R Dunne, K Brady; N Murray, K Clarke, C Moynagh; G McKiernan, T Corr; M Reilly, D McVeety, N Clerkin; G Smith, C Madden, S Johnston.
Subs: C Mackey for Johnston (45), C Brady for Clerkin (61), J McCutcheon for Madden (62), P O’Connor for Corr (71).
Ref - A Nolan (Wicklow)
I caught up with the Shane Williams-Michael Murphy sport-swapping documentary last week. When Williams, once the world's number one rugby player, took to the field for his debut against Convoy, the blizzard was so heavy you could barely see the ball for the snow.
It was a meat and two veg day at Croke Park on Friday, but it produced scenes of unconfined joy. And that even applied to the men who have mined on the county stage, especially Colm 'Gooch' Cooper, the mascot of 25 years ago and now the hometown hero.