The win extended the Robins’ unbeaten run to 12 matches – they have lost only five games all season – and returns them to the Championship after a two-year absence. It was their 12th away win and Bradford’s fourth defeat in five matches.
He said: “Obviously, we are pleased to win promotion and now we want to go on and win the title.
“We have played open and expansive football all season and there is a good tempo to our play. We have taken risks and sometimes we have been caught, but we have played good football and entertained crowds throughout the country.
“We don’t go anywhere just to get a point and to change our DNA now – tonight – would have been dangerous.
“We have got a really united bunch of players and we have enjoyed the celebrations on the pitch tonight, but our main aim this season has been to win the League One title.”
Bradford-born James Tavernier and Joe Bryan gave Bristol City a 2-0 half-time lead before the visitors ran riot in the second period – Tavernier completing his double and Luke Ayling, Aden Flint and Aaron Wilbraham all netting.
Cotterill added: “We just played well tonight. The 22 players out there have played 109 games this season and although tonight is our night, I don’t think we should overlook what a great season Bradford City have had with their run to the quarter-final of the FA Cup, beating Sunderland and Chelsea along the way.
“So we knew what a difficult game it was going to be.
“It was a fantastic atmosphere and even when we were winning the Bradford fans were first class. They have had a fantastic season.”
Bradford manager Phil Parkinson said: “Congratulations to Bristol City. They are an outstanding team, full of confidence and we just couldn’t handle them tonight, although we have beaten better teams than them in cup competitions this season.
“It is probably the worst defeat I have had in four years as Bradford City manager. We have had plenty of good times, but tonight is a low point. There are no excuses for that performance.
“That said, we have got to rally the troops and be ready to go again. We have four matches left and reputations are at stake.
“We didn’t do the basics in our defending. We said at half-time when we were 2-0 down,
‘Let’s make sure we don’t concede again’, but we got worse and the third goal killed us.
“The players, who have played so well for us this season have performed so poorly on the same night. Why? I can’t be sure.
“One thing we have always done is stand up and be counted and defended well, but tonight we didn’t do any of those things and I have to take responsibility.”