Stephen Griffin's stoppage-time equaliser against Mayo sealed Donegal's passage to the Football League Division One semi-finals.
Substitute Griffin pounced in the fifth minute of added time to secure the point which puts then through to a meeting with Cork next weekend.
Rory Gallagher's team had led 1-5 to 0-7 at half-time at Castlebar thanks to Patrick McBrearty's 19th-minute goal.
McBrearty thought he had scored a second goal but it was disallowed.
That incident came in the second half when substitute Anthony Thompson sent a long ball forward.
McBrearty put the ball into the net but was penalised for pushing.
Donegal's Odhrán MacNiallais scored three points in the first half and was one of the Ulster county's best performers.