Blair was sent off early in the second half and substitute Jordan Flores stole the points with a stoppage-time penalty, the visitors’ second of the afternoon.
“The game changes on the red card,” reflected Ferguson, who saw his side lose for only the second time at home this season.
“He’s given it quite quickly considering Matty went down injured. I can see why he gave the first one [penalty], although it’s still dubious, but the second one is outside the box.
“The second is outside the box, no doubt about it.
“Once you’ve given one, you’d like to think he’d have to be absolutely certain to give another so quickly after it.”
In the first half the hosts were denied as Sam Slocombe thwarted Joe Wright and Alfie May.
Seven minutes into the second half Rovers were down to 10 men after a second booking for Blair.
Three minutes from time Blackpool got their first penalty for handball, but Marko Marosi flicked Cullen’s effort onto a post.
Moments later the Tangerines had a second bite of the cherry and Flores made no mistake after taking over from Cullen.
Doncaster Rovers: Marosi, Alcock, Baudry, Wright, Taylor-Sinclair (McSheffrey, 63), Mason, Blair, Grant (Longbottom, 71), Rowe, Marquis, May (Middleton, 55). Unused substitutes: Jones, Lund, Keegan, Beestin.
Blackpool: Slocombe, Mellor, Aldred, Aimson, Robertson, Taylor, Potts, Payne (Flores, 49), Danns (Cullen, 63), Black, Delfouneso (Matt, 69). Unused substitutes: Lyness, Osayi-Samuel, Odelusi, Nolan.
Referee: Carl Boyeson (East Yorkshire).