Teenager Simon Wiles scored the only goal of the game six minutes from time while the Seasiders played with 10 men for 54 minutes after veteran full-back Rob Edwards was sent off.
A win was vital after Blackpool's terrible start to the season, which had raised questions about Hendry's position.
The ex-Iron managerial target said: "I said my job was on the line if I did not see three points from this game. We got the three points."