The 24-year-old came off the bench to give the Blues all three points with a delightful 25-yard free-kick four minutes from time.
It was a timely reminder of the potential of Naismith, a player whose days at Fratton Park looked numbered in the summer when he was put on the transfer list.
Cook reversed that decision in September – and has challenged the Glaswegian to keep on proving he made the right move.
‘Kal deserves a massive pat on the back,’ said Cook. ‘I don’t want to single players out in general but he’s been on the transfer list, he’s been kicked from pillar to post, he’s been dragged off, he’s been put on – but that’s an amazing goal.
‘He’s got such talent. Kal needs to start showing that more regularly. When he does, he’ll be a player I’m sure our supporters will come to admire.’
Naismith, along with Conor Chaplin and Noel Hunt, was one of three attacking substitutions Cook was able to make on Saturday as Pompey looked to find the breakthrough their dominance deserved.
With Pompey often getting the better of opponents but at times left frustrated in search of a goal, Cook believes being able to call on a rich array of talent from the bench could keep proving crucial.
The Blues boss said: ‘I think when you’ve got the bench we have – Lalkovic, Chaplin, Naismith, these type of players, then I’m sure there’s a goal in us.
‘We know we’ve got a talented squad and we will need everyone of them at some stage during the season.
‘We’ve seen it plenty of times before. We may struggle to get that goal our play deserves but we are always confident of nicking a goal because of the calibre of player we have.
‘It’s great for me to be able to have that choice.’
Cook had no doubt his team deserved to come away from Blundell Park with the win, even after Grimsby raised their game in the second half.
He said: ‘We were by far the most dominant team, in my opinion.
‘Great credit to our players. In the first half, we were excellent. That’s the best we’ve played for a bit.
‘When the players play like that it becomes a marriage made in heaven.
‘Grimsby are a good side – they’ve got threats, they put us under pressure in the second half but the lads stood up to it.
‘It was a great result for us.’
– HOWARD FROST