After a lacklustre first half against relegation threatened Barnet, Cook revealed he laid in to his players at the break demanding they treat the game like a cup final to keep touch with the top seven.
And he got the response he wanted as first Jay O'Shea and then Sam Togwell found the back of the net to put Chesterfield within three points of seventh-placed Exeter.
"We didn't play well," the former Accrington boss said of his team's first-half display. "The first half was probably as poor as I've seen us play. It looked like an end of season game when we had nothing to play for and the paint came off the walls at half time.
"(In the) second half we improved and got a couple of good goals and played a lot better.
"The message at half time was liven up. The pleasing thing was we dug in and I thought we finished the second half quite well.
"At the minute every game is a big pressure game for us. If we get beat it's like the end. We have four games left and all of a sudden we seem to have a lot to play for. But what we have to play for is next Saturday against Bradford and that's the only game in my mind.
"This was a big one, all games are big and there's none bigger that Bradford for us next week."