It was all set to be a close and exciting encounter between two sides battling for promotion to the Championship.
And Pompey’s Fratton fixture against Lincoln certainly began at a fair pace, with both sides looking to launch quick attacks.
But the game turned on a big decision by referee Sam Purkiss, who showed Jack Whatmough a straight red card for a challenge on Jorge Grant.
It was a decision that perplexed the defender, most others inside the ground and those fans watching from home.
The visitors went on to break Pompey’s brave resistance through a late Morgan Rogers strike and Jackett was disappointed with the dismissal.
The Blues boss said: “I was expecting a yellow card and was surprised to see a red. Up until that point, it was an even game.
"The sending off was the big incident and we will be appealing the decision. It’s quite clear on the replay that he got the ball."
“There were two good teams and we were trying to get our attacking players on the ball on a slick pitch.
“But the sending off was the big incident and we will be appealing the decision. It’s quite clear on the replay that he got the ball.
“I was pleased with my team and proud of the effort that they put in – we were unlucky not to get a goal or a decision in their box.
“The players felt we should have had a penalty and it’s whether their guy’s hand – which was above his head – was in an unnatural position.
“It was a frustrating result in a vastly different game from Saturday and now we have to work hard to close the gap between ourselves and the top.
“We have to recognise what we can learn from defeats and we’ve got some work to do to get where we want to be.”
The game capped a difficult few days for Whatmough, who netted two unfortunate own-goals against Hull at the weekend.
Jackett said: “Jack has certainly had worse days in his career with the injuries he’s suffered in the past.
“First and foremost, though, he’s a very good footballer and with the character he’s got, he’ll bounce back from this.