Donaldson netted to cancel out Paul Green's opener and leave Steve Tilson's men still looking for their first win in seven games.
Crewe almost broke the deadlock when Joel Grant played a fine one-two with Donaldson before unleashing a low drive which was parried by Elliot Parish into the path of Shaun Miller, who could not direct his header on target.
The visitors took the lead two minutes after the break when Danny Hone headed a corner back across goal, allowing Green to swivel and strike the ball in via the post.
But Donaldson fired Crewe level in the 76th minute from the penalty spot after Hone dragged back Ashley Westwood in the box.
Gavin McCallum went close to a winner for the Imps but fired wide and saw another effort blocked by Lee Bell before Ben Hutchinson headed over from five yards out at the death.
Source: PA
Source: PA