It was a moment of real quality that settled an otherwise scrappy contest on the Fylde coast.
John Marquis dived to head home a Ryan Williams cross in the first and seal all three points for Pompey at Fleetwood.
The hosts dominated possession in the second half, but Craig MacGillivray was never called into any serious action.
And Kenny Jackett was delighted with the solidity of his troops, as they kept pressure on the League One automatic promotion places.
The Blues boss said: “It was a great win for us and the side showed fantastic character, working really hard to keep a clean sheet.
“Ultimately, the game was decided by a quality goal, with a great cross from Ryan and a terrific header from John.
“He got the ball down and gave the keeper absolutely no chance – it was that moment that decided the game.
“You need that defensive solidity we’ve shown of late, while also being able to score goals – and we got a great one in this game.
“Fleetwood had one long-range shot in the second half that went into Craig’s midriff, but other than that, they haven’t created a chance.
"He got the ball down and gave the keeper absolutely no chance – it was that moment that decided the game."
“We had one big opportunity through Michael Jacobs soon after the break, but their keeper made a big save.
“That was the sum total of a second period that never really got going – but that suited as the side who had the lead.
“We never looked rusty and the players are enjoying their football, which is good news with so many games coming up.
“It will be good to get back to Fratton Park for the next three matches and hopefully we can capitalise on that.”
Teams are currently allowed to make five substitutes, but Jackett opted not to use anyone from the bench.
He explained: “We were in a good rhythm and routine, while my front four players were posing a threat on the break, so I didn’t want to take them off.”