Marcus Harness was on the scoresheet at Griffin Park against the side who are chasing a place in the Premier League.
Brentford levelled from the penalty spot in the second half in a game which saw young keeper Duncan Tunbull unusually turn out for the home side.
The Bees may have been in action yesterday, but the result represents a decent return for Pompey with their opponents recently defeating Arsenal.
John Marquis almost put Jackett’s side in front in the opening seconds before Ross McCrorie crossed for Harness to head home in the 14th minute.
The reply came in the second half when Mads Roerslev was tripped in the box and Halil Dervisoglu sent Alex Bass the wrong way from the spot.
An injury to Nathan Sheppard then saw Turnbull go between the sticks for Brentford and he excelled there when denying Gareth Evans.
Paul Downing then headed wide late on for the Blues.
The result follows on from Pompey being defeated by Reading last week in their first game back since returning to training amid the coronavirus pandemic.
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