But calm increasingly descended across the Pompey manager as he preached his mantra of remaining grounded.
‘I don’t want to get involved in talk about cushions,’ he said, as he surveyed the four-point gap opening up between the men who’d just served up the most powerful attacking display on the road of his Fratton tenure and fourth place.
‘We don’t need a cushion - we need a sofa!’
All around him his appeals for remaining on an even keel went gloriously unheeded.
Sixty yards to his right, 2,244 jubilant Pompey fans were endlessly belting out their ‘we’re on our way’ anthem on two sides of the Weston Homes Community Stadium.
Away in the corporate section, nicely-oiled Blues followers sung, smiled and swayed on the balconies of their boxes.
And behind Cook in the directors’ box, chairman Iain McInnes charged around savouring the occasion with the board and their grinning guests documenting the moment on social media.
We’ve been here often enough to know better, of course, but this really felt like the moment.
March 11, 2017: The day Pompey grasped the opportunity and seized their promotion fate.
Everywhere you turned royal blue bloods were saucer-eyed with glorious belief; drunk on the reality destiny was back in the hands of their team once again.
A display of attacking force which increasingly battered Colchester into submission was the reason for that.
For seven minutes or so, it looked like Cook’s men were going to have to stand toe-to-toe with a foe who’d won seven of their last eight contests on their own patch.
‘I thought we’re going to be in for a game here,’ reflected assistant Leam Richardson, of his thoughts in those early moments.
Pompey gradually exerted their control, however, as the excellent Carl Baker teased a deliver into exactly the area defences hate. Eoin Doyle was well placed but couldn’t make a connection, and would’ve been pleased to see the offside flag go up in any event.
That moment, however, signalled the start of the Blues’ unerring, unrelenting attacking charge. And Colchester simply had no answer.
By the time striker Doyle had headed his side in front in the 22nd minute, Kal Naismith, Enda Stevens and the striker himself had carved out other opportunities.
Frustration mounted at first, as Naismith continued Pompey’s penchant for failing to get a corner beyond the first man. The Scot, who is undoubtedly in the form of his Fratton career, didn’t need to be asked a second time, though, as he dangled a ball on to Doyle’s head.
Much has been made of a testing start to his loan, after being feted as the man to make the difference to Cook’s side this season. Doyle’s nod through Sam Walker sparked the kind of celebratory release which told what the moment meant to the 28-year-old. Likewise, the way he was mobbed by his team-mates was revealing.
So, four days on from missing a penalty at Crawley, and being informed it was ‘now or never’ by a travelling supporter just before he stepped up, Doyle had lift off.
While sections of support spoke of Cook bringing in another Michael Smith, the former Cardiff man’s positional play gave cause for optimism the net would soon be found.
His goal ratio is not the only yardstick his manager is measuring him by, though.
Doyle’s ability to create space and chances for his team-mates is a fundamental objective of Cook’s lead man in his preferred 4-2-3-1 formation. And so we saw just 33 seconds after the restart as Kyle Bennett’s second in as many games put the game to bed.
The striker’s pressure on George Elokobi brought a rushed clearance which was feasted on by Naismith. A typically nonchalant no-look pass to the penalty spot had Bennett applying the finish.
From there, the margin of victory could have been anything.
With the shackles off, Pompey were operating with the kind of fluency and freedom which makes them very difficult to contend with at this level.
Players interchanged positions seamlessly. Flicks found their targets effortlessly. Full-backs overlapped with vibrancy. And deep-lying runners popped up constantly. Still, few would have backed the Blues’ holding midfielders to be the men to apply the gloss on an afternoon to remember.
It was Eoin Doyle’s creative quality which unlocked Colchester for the umpteenth time after 61 minutes. Danny Rose capped a second outstanding display on the bounce with an ice-cool dink at the second attempt.
The best was yet to come, however, as the romp was rounded off with a swagger.
Pompey’s fourth was one for the purists. The pace at which the counter-attack unfolded. The vision of Eoin Doyle. The impudent weight and foresight of Bennett’s pass. And the desire of Naismith to join the party with his charge through the middle.
The fact Walker’s parry from Naismith’s finish was sniffed out by Michael Doyle, of all people, just added to the story.
And there were so many angles to savour from this tale, it was hard to know quite where to start.
Eoin Doyle’s man-of-the-match emergence, Naismith’s majesty, Baker’s verve, Bennett’s frills, goal-scoring defensive midfielders and a 17th clean sheet of the campaign.
It was the kind of perfect afternoon which had echoes of the championship-winning party at Bradford in 2003.
And you have to go back to that exultant day at Valley Parade for a bigger margin of victory on the road from Pompey, as the 6-2 success at Cambridge two years ago and 4-0 romp at Middlesbrough in 2006 was equalled.
Yes, the notes of caution were Colchester’s crippling injury list and the question of repeating back-to-back away wins as we return to Fratton on Tuesday night.
But the U’s home form and place on the edge of the play-off battle suggested they were handling their problems admirably before being decimated.
And, for all the suffocating expectancy and angst detected on their own patch of late, there are the countless memories of night’s under the Fratton lights to savour.
Another of those would confirm what we all felt in the spring Essex sunshine, and have League One listening to the growing intensity of the message: Pompey are on their way.