The former Portsmouth fans favourite had been in prolific pre-season form since his sensational arrival in the ninth tier of English football.
And after nine goals in friendly action, Pitman headed in a 77th minute winner to get the pre-season Wessex Premier title favourites off to a triumphant start.
Pitman showed great movement to make himself a yard of room to nod in a left-wing cross.
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‘It was a difficult first game,’ said assistant boss Gavin Spurway. ‘Maybe there were a bit of nerves. The first game is always a bit nervy, whatever anyone says.
‘Cowes defended well, but I always felt we were going to score, we were creating chances. It was the sort of game last season that we might not have ended up winning.
‘That’s why we signed Brett Pitman, to do what he does.’
Pitman, 34, has hit the ground running at Portchester after being released by Bristol Rovers at the end of last season.
Last night’s header was his first competitive goal since netting for Eastleigh in a 5-3 National League loss at Solihull in March during a loan spell.
‘He’s come in, he listens, he’s got his head down, he wants to be involved in everything, he speaks to the players, gives them advice,’ Spurway added.
‘I’ve been nothing but impressed with him so far. He’s given 110 per cent and he’s scored goals - that’s the main reason we signed him. If you give him chances, he will score. He had two last night and scored once - long may it continue.’
Portchester started with another new signing, ex-Bognor and Gosport player Ashton Leigh, in a three-man backline alongside Sam Pearce and Curt Da Costa. Pitman partnered Felipe Barcelos up front.
Spurway had to make an early change when Tyler Giddings, who was playing right midfield, went off with a calf injury. Liam Robinson came in for a direct swap.
Midfielder Marley Ridge was sick at half-time, so was replaced by George Barker.