Rochdale’s loss to MK Dons confirmed Chesterfield ‘s top-six finish, even though their seven-game unbeaten run was ended by another impressive display from Cotterill’s side.
There was little between the teams until Chesterfield lost the ball outside the penalty area in the 31st minute and Kieran Agard went past Sam Hird to place a low shot beyond Tommy Lee.
Then Aden Flint climbed at the back of the six-yard box to head in a corner for his 12th goal of the season as City ran out deserved winners.
“I’ve been proud of these boys quite a few times this season but today I’m probably prouder of them,” Cotterill said.
“It’s easy to be proud when you win at Wembley and win the title but when you then have to come to a difficult venue like this it’s ‘are they going to be turn up? Are they going to play properly? Are they going to be committed?’ And they were every single one of those.
“I thought I knew the boys and I hoped they would put in that type of performance because whilst it was still mathematically possible for another team to get in the play-offs you have to do right by Rochdale and I felt we did that.
“It’s always important for the manager that they continue even when we can’t really achieve any more now and I’m really proud of the boys, they are everything I thought they were – real, honest, fantastic professionals.”
Chesterfield assistant manager Leam Richardson admitted his players were disappointed despite making the play-offs.
He added: “It’s a bit subdued and a bit flat because you want to win games and with the standards we’ve got we wanted to go unbeaten to the end of the season and hopefully to Wembley and through that.
“We are disappointed we didn’t win but I thought it was a great game, very tactical and you’ve got to give Bristol City loads of compliments; they played well and they’ve got the depth and the knowledge and you can see why they are champions.
“Our lads never give up and that’s why they find themselves in the position they are in today. They’ve had a great season so far and hopefully we can kick on and make it a fantastic one.”