The Pompey boss feels the 4-0 romp over the U’s last month was the crucial win of the campaign.
Cook highlighted the relentless nature of the success over their play-off-chasing rivals as a line in the sand when it came to the Blues’ promotion bid.
The poor home loss to Crewe is highlighted as a key result by many, as it proved the precursor for a run of one loss in 10.
Cook feels the manner in which Pompey clicked in Essex told his team what they could achieve, however.
He said: ‘People go on about the Crewe game being the turning point.
‘I think it was the Colchester game which was the turning point. That’s my honest opinion.
‘That was the first time we looked the team we all wanted to be.
‘Crewe’s part of football – everyone gets beat. It’s footie.
‘If we didn’t get beat by Crewe, though, it would have been one defeat in 16.
‘I felt Colchester was the game where we had great support and also played really, really well.
‘We just looked a very strong team that day – by beating a very strong team on their own patch.
‘There was then that feel-good factor for the lads.
‘The Crawley win was a good win and the Crewe game gets talked about.
‘I think the Colchester game was a catalyst to us actually believing we can’t be messing around with what we’re doing, though.
‘We realised it’s now our time – and I think the results show it is our time.’
Despite progressing from last season’s play-off disappointment, Cook feels there is no big secret about his side’s improvement this term.
He reckons personnel has made a major difference.
Cook added: ‘People will say we have had a change of mindset and different stuff. We haven’t.
‘Our lads train the same way, we prepare the same way and we set the team up the same way. We’ve done nothing different this season.
‘Along the way people say the reasons why. We haven’t done anything differently. I’d love to say we have.
‘I just think some of the personnel have come in and helped.
‘If you look at David Forde, for example, we don’t concede last-minute goals from balls into the box now. That’s what he was brought in for.
‘People were brought in with a job spec – and they’ve done it.
‘We think it’s important we keep improving.
‘We’ve had different strikers. A criticism is we haven’t got a 20-goal striker, but we score enough goals to win games.
‘It’s all about personnel.
‘The biggest compliment is these players get knocked down, but get up and keep going.’